Wood Preservation Stan T

Home , Framing (construction), Hardwood, Lumber, Sawdust, Wood preservation

CHAPTER 15

Wood Preservation Stan T. Lebow, Research Forest Products Technologist

Many commonly used wood species can deteriorate if exposed to conditions that support growth of wood-degrading Contents organisms (see Chap. 14). Wood products can be protected Wood Preservatives 15–1 from the attack of decay fungi, harmful insects, or marine Waterborne Preservatives 15–3 borers by applying chemical preservatives. Preservative Preservatives with ICC–ES Evaluation treatments greatly increase the life of wood structures, thus Reports 15–9 reducing replacement costs and allowing more efficient Oil-Borne or Oil-Type Preservatives 15–10 use of forest resources. The degree of protection achieved depends on the preservative used and the proper penetration Treatments for Wood Composites 15–12 and retention of the chemicals. Some preservatives are more Water-Repellent and Nonpressure effective than others, and some are more adaptable to certain Treatments 15–12 use requirements. To obtain long-term effectiveness, ad- Selecting Preservatives 15–12 equate penetration and retention are needed for each wood Evaluating New Preservatives 15–13 species, chemical preservative, and treatment method. Not only are different methods of treating wood available, but Preservative Effectiveness 15–13 treatability varies among wood species—particularly their Effect of Species on Penetration 15–15 heartwood, which generally resists preservative treatment Preparation of Wood for Treatment 15–15 more than does sapwood. Although some tree species pos- Peeling 15–15 sess naturally occurring resistance to decay and insects (see Chap. 14), many are in short supply or are not grown Drying 15–16 in ready proximity to markets. Conditioning of Green Products 15–17 In considering preservative treatment processes and wood Incising 15–17 species, the combination must provide the required protec- Cutting and Framing 15–18 tion for the conditions of exposure and life of the structure. Application of Preservatives 15–18 All these factors are considered by the consensus techni- Pressure Processes 15–18 cal committees in setting reference levels required by the American Wood Protection Association (AWPA, formerly Effect on Mechanical Properties 15–20 American Wood-Preservers’ Association)) and ASTM Inter- Nonpressure Processes 15–20 national (formerly American Society for Testing and Materi- In-Place and Remedial Treatments 15–22 als). Details are discussed later in this chapter. The charac- Best Management Practices 15–23 teristics, appropriate uses, and availability of preservative formulations may have changed after preparation of this Quality Assurance for Treated Wood 15–25 chapter. For the most current information on preservative Treating Conditions and Specifications 15–25 formulations, the reader is encouraged to contact the appro- Inspection of Treatment Quality 15–25 priate regulatory agencies, standardization organizations, or Effects on the Environment 15–26 trade associations. Note that mention of a chemical in this chapter does not constitute a recommendation. Recycling and Disposal of Treated Wood 15–26 References 15–27 Wood Preservatives Wood preservatives must meet two broad criteria: (1) They must provide the desired wood protection in the intended end use, and (2) they must do so without presenting unrea- sonable risks to people or the environment. Because wood preservatives are considered to be a type of pesticide, the U.S. Environmental Protection Agency (EPA) is responsible for their regulation. Federal law requires that before selling or distributing a preservative in the United States,

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a company must obtain registration Synopsis of EPA-approved consumer information sheets for wood treated with from EPA. Before registering a new CCA, ACZA, creosote, or pentachlorophenol pesticide or new use for a registered preservative, EPA must first ensure NOTE: This is only a synopsis of information contained in consumer information sheets. For complete consumer information sheets, contact your treated wood supplier that the preservative can be used with or the website of the Environmental Protection Agency. a reasonable certainty of no harm to human health and without posing un- Handling Precautions reasonable risks to the environment. Avoid frequent or prolonged inhalation of sawdust from treated wood. When sawing, To make such determinations, EPA sanding, and machining treated wood, wear a dust mask. Whenever possible, these requires more than 100 different scien- operations should be performed outdoors to avoid indoor accumulations of airborne tific studies and tests from applicants. sawdust from treated wood. When power-sawing and machining, wear goggles to This chapter discusses only wood pre- protect eyes from flying particles. Wear gloves when working with the wood. After servatives registered by the EPA. working with the wood, and before eating, drinking, toileting, and use of tobacco products, wash exposed areas thoroughly. Avoid frequent or prolonged skin contact Some preservatives are classified as with creosote- or pentachlorophenol-treated wood. When handling creosote- or pen- “restricted use” by the EPA and these tachlorophenol-treated wood, wear long-sleeved shirts and long pants and use gloves can be used only in certain applica- impervious to the chemicals (for example, gloves that are vinyl coated). Because tions and can be applied only by certi- preservatives or sawdust may accumulate on clothes, they should be laundered before fied pesticide applicators. Restricted reuse. Wash work clothes separately from other household clothing. use refers to the chemical preservative Treated wood should not be burned in open fires or in stoves, fireplaces, or residential and not to the treated wood prod- boilers, because toxic chemicals may be produced as part of the smoke and ashes. uct. The general consumer may buy Treated wood from commercial or industrial use (such as construction sites) may be and use wood products treated with burned only in commercial or industrial incinerators or boilers in accordance with restricted-use pesticides; EPA does state and Federal regulations. CCA-treated wood can be disposed of with regular not consider treated wood a toxic municipal trash (municipal solid waste, not yard waste) in many areas. However, state or local laws may be stricter than federal requirements. For more information, please substance nor is it regulated as a pes- contact the waste management agency for your state. ticide. Although treated wood is not regulated as pesticide, there are limita- Use Site Precautions tions on how some types of treated All sawdust and construction debris should be cleaned up and disposed of after con- wood should be used. Consumer In- struction. Do not use treated wood under circumstances where the preservative may formation Sheets (EPA-approved) are become a component of food or animal feed. Examples of such sites would be use of available from retailers of creosote-, mulch from recycled arsenic-treated wood, cutting boards, counter tops, animal bed- pentachlorophenol-, and inorganic- ding, and structures or containers for storing animal feed or human food. Only treated arsenical-treated wood products. The wood that is visibly clean and free of surface residue should be used for patios, decks, and walkways. Do not use treated wood for construction of those portions of beehives sheets provide information about the which may come into contact with honey. Treated wood should not be used where it preservative and the use and disposal may come into direct or indirect contact with drinking water, except for uses involv- of treated-wood products (see Syn- ing incidental contact such as docks and bridges. opsis of EPA-Approved Consumer Information Sheets for Wood Treated Logs treated with pentachlorophenol should not be used for log homes. Wood treated with CCA, ACZA, Creosote, or Pen- with creosote or pentachlorophenol should not be used where it will be in frequent or prolonged contact with bare skin (for example, chairs and other outdoor furniture), tachlorophenol). The commercial unless an effective sealer has been applied. Creosote- and pentachlorophenol-treated wood treater is bound by the EPA wood should not be used in residential, industrial, or commercial interiors except for regulation and can treat wood only laminated beams or building components that are in ground contact and are subject to for an end use that is allowed for that decay or insect infestation and where two coats of an appropriate sealer are applied. preservative. Some preservatives that Do not use creosote- or pentachlorophenol-treated wood for farrowing or brooding are not classified as restricted by EPA facilities. Wood treated with pentachlorophenol or creosote should not be used in the are available to the general consumer interiors of farm buildings where there may be direct contact with domestic animals for nonpressure treatments. It is the or livestock that may crib (bite) or lick the wood. In interiors of farm buildings where responsibility of the end user to apply domestic animals or livestock are unlikely to crib (bite) or lick the wood, creosote- or these preservatives in a manner that is pentachlorophenol-treated wood may be used for building components that are in consistent with the EPA-approved la- ground contact and are subject to decay or insect infestation and where two coats of an appropriate sealer are applied. Sealers may be applied at the installation site. Ure- beling. Registration of preservatives is thane, shellac, latex epoxy enamel, and varnish are acceptable sealers for pentachlo- under constant review by the EPA, and rophenol-treated wood. Coal-tar pitch and coal-tar pitch emulsion are effective sealers a responsible State or Federal agency for creosote-treated wood-block flooring. Urethane, epoxy, and shellac are acceptable should be consulted as to the current sealers for all creosote-treated wood. status of any preservative.

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Before a wood preservative can be approved for pressure to leaching and very good performance in service. Water- treatment of structural members, it must be evaluated to borne preservatives are included in specifications for items ensure that it provides the necessary durability and that it such as lumber, timber, posts, building foundations, poles, does not greatly reduce the strength properties of the wood. and piling (Table 15–1). Because water is added to the wood The EPA typically does not evaluate how well a wood pre- in the treatment process, some drying and shrinkage will servative protects the wood. Traditionally this evaluation occur after installation unless the wood is kiln-dried after has been conducted through the standardization process of treatment. the AWPA. The AWPA Book of Standards lists a series of Copper is the primary biocide in many wood preservative laboratory and field exposure tests that must be conducted formulations used in ground contact because of its excellent when evaluating new wood preservatives. The durability of fungicidal properties and low mammalian toxicity (Table test products are compared with those of established durable 15–3). Because some types of fungi are copper tolerant, pre- products and nondurable controls. The results of those tests servative formulations often include a co-biocide to provide are then presented to the appropriate AWPA subcommittees further protection. for review. AWPA subcommittees are composed of represen- tatives from industry, academia, and government agencies Inorganic arsenicals are a restricted-use pesticide. For use who have familiarity with conducting and interpreting dura- and handling precautions of pressure-treated wood contain- bility evaluations. Preservative standardization by AWPA is ing inorganic arsenicals, refer to the EPA-approved Con- a two-step process. If the performance of a new preservative sumer Information Sheets. is considered appropriate, it is first listed as a potential pre- Acid Copper Chromate (ACC) servative. Secondary committee action is needed to have the new preservative listed for specific commodities and to set Acid copper chromate (ACC) contains 31.8% copper oxide the required treatment level. and 68.2% chromium trioxide (AWPA P5). The solid, paste, liquid concentrate, or treating solution can be made of cop- More recently the International Code Council–Evaluation per sulfate, potassium dichromate, or sodium dichromate. Service (ICC–ES) has evolved as an additional route for Tests on stakes and posts exposed to decay and termite at- gaining building code acceptance of new types of pressure- tack indicate that wood well impregnated with ACC gener- treated wood. In contrast to AWPA, the ICC–ES does not ally provides acceptable service. However, some specimens standardize preservatives. Instead, it issues Evaluation Re- placed in ground contact have shown vulnerability to attack ports that provide evidence that a building product complies by copper-tolerant fungi. ACC has often been used for treat- with building codes. The data and other information needed ment of wood in cooling towers. Its current uses are re- to obtain an Evaluation Report are first established as Ac- stricted to applications similar to those of chromated copper ceptance Criteria (AC). AC326, which sets the performance arsenate (CCA) (Table 15–4). ACC and CCA must be criteria used by ICC–ES to evaluate proprietary wood pre- used at low treating temperatures (38 to 66 °C (100 to servatives, requires submittal of documentation accredited 150 °F)) because they are unstable at higher temperatures. third party agencies in accordance with AWPA , ASTM, and This restriction may involve some difficulty when higher EN standard test methods. The results of those tests are then temperatures are needed to obtain good treating results in reviewed by an evaluation committee to determine if the woods such as Douglas-fir. preservative has met the appropriate acceptance criteria. Ammoniacal Copper Zinc Arsenate (ACZA) Wood preservatives have traditionally been divided into Ammoniacal copper zinc arsenate (ACZA) is commonly two general classes: (1) Oil-type or oil-borne preservatives, used on the West Coast of North America for the treatment such as creosote and petroleum solutions of pentachloro- of Douglas-fir. The penetration of Douglas-fir heartwood phenol, and (2) waterborne preservatives that are applied as is improved with ACZA because of the chemical composi- water solutions or with water as the carrier. Many different tion and stability of treating at elevated temperatures. Wood chemicals are in each of these classes, and each has different treated with ACZA performs and has characteristics similar effectiveness in various exposure conditions. Some preser- to those of wood treated with CCA (Table 15–1). vatives can be formulated so that they can be delivered with either water or oil-type carriers. In this chapter, both oil- ACZA should contain approximately 50% copper oxide, borne and waterborne preservative chemicals are described 25% zinc oxide, and 25% arsenic pentoxide dissolved in a as to their potential end uses. Tables 15–1 and 15–2 sum- solution of ammonia in water (AWPA P5). The weight of marize preservatives and their treatment levels for various ammonia is at least 1.38 times the weight of copper oxide. wood products. To aid in solution, ammonium bicarbonate is added (at least equal to 0.92 times the weight of copper oxide). Waterborne Preservatives Waterborne preservatives are often used when cleanliness ACZA replaced an earlier formulation, ammoniacal copper and paintability of the treated wood are required. Formula- arsenate (ACA) that was used for many years in the United tions intended for use outdoors have shown high resistance States and Canada.

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Table 15–1. Typical use categories and retentions for preservatives used in pressure treatment of Southern Pine speciesa Retentions (kg m–3)b for each type of exposure and AWPA use category designation Exterior Soil or above-ground fresh water Interior, dry or Vertical, Severe/ Very severe/ damp coated Horizontal General critical critical Preservative 1, 2 3A 3B 4A 4B 4C 4C (piles) Waterborne: Listed by the AWPA ACC NLc NLc 4.0 8 — — — ACZA 4.0 4.0 4.0 6.4 9.6 9.6 — ACQ–B 4.0 4.0 4.0 6.4 9.6 9.6 — ACQ–C 4.0 4.0 4.0 6.4 9.6 9.6 — ACQ–D 2.4 2.4 2.4 6.4 9.6 9.6 — CA–B 1.7 1.7 1.7 3.3 5.0 5.0 — CA–C 1.0 1.0 1.0 2.4 5.0 5.0 — CBA–A 3.3 3.3 3.3 6.5 9.8 9.8 — CCA NLc NLc 4 6.4 9.6 9.6 12.8 CX–A 3.3 3.3 3.3 — — — — CuN (waterborne) 1.12 1.12 1.12 1.76 — — — EL2 0.30 0.30 0.30 — — — — KDS 3.0 3.0 3.0 7.5 — — — PTI 0.21 0.21 0.21/0.29d — — — — SBX 2.8/4.5e — — — — — — Oil-type: Listed by the AWPA Creosote 128/NRf 128.0 128.0 160 160 192 192 Penta P9 Type A Oil 6.4/NRf 6.4 6.4 8.0 8.0 8.0 9.6 Penta P9 Type C Oil 6.4/NRf 6.4 6.4 8.0 8.0 8.0 9.6 CuN (oilborne) 0.64/NRf 0.64 0.64 0.96 1.2 1.2 1.6 Cu8 0.32 0.32 0.32 — — — — Waterborne: Evaluation reports from ICC Evaluation Service, Inc. ESR–1721 0.8 0.8 0.8 2.2 3.6 5.3 5.3 ESR–1980 2.4 2.4 2.4 5.4 9.6 9.6 — ESR–2067 0.3 0.3 0.3 — — — — ESR–2240 1.0 1.0 1.0 2.4 3.7 ESR–2325 1.1 1.1 1.1 2.6 3.8 — — ESR–2711 2.1/2.7g 2.1/2.7g 2.1/2.7g 4.5 6.9 — — aSome exceptions exist for specific applications. See AWPA Standard U1 or ICC ES Evaluation Reports for details on specific applications. See Table 15–2 for seawater applications. bTo convert to retention expressed as lb ft–3, divide these values by 16.0. cNL, not labeled. EPA labeling does not currently permit use of wood newly treated with these preservatives in most applications within these use categories. See Table 15–4 for more details. dHigher retention specified if the preservative is used without a stabilizer in the treatment solution. eHigher retention for areas with Formosan subterranean termites. fNR, not recommended for interior use in inhabited structures. g 2.1 kg m–3 retention limited to decking and specialty use items.

Chromated Copper Arsenate (CCA) this labeling change and that the EPA has not recommended Wood treated with CCA (commonly called green treated) removing structures built with CCA-treated lumber. These dominated the treated-wood market from the late 1970s changes were made as part of the ongoing CCA re-registra- until 2004. However, as the result of the voluntary label tion process, and in light of the current and anticipated mar- changes submitted by the CCA registrants, the EPA labeling ket demand for alternative preservatives for nonindustrial of CCA currently permits the product to be used for primar- applications. Allowable uses for CCA are based on specific ily industrial applications (Table 15–4), and CCA-treated commodity standards listed in the 2001 edition of the AWPA products are generally not available at retail lumber yards. standards. The most important of these allowable uses are CCA can no longer be used for treatment of lumber intended based on the standards for poles, piles, and wood used in for use in residential decks or playground equipment. It is highway construction. A list of the most common allowable important to note that existing structures are not affected by uses is shown in Table 15–4.

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Although several formulations of CCA have been used in for copper oxide; and arsenic acid, sodium arsenate, or the past, CCA Type C has been the primary formulation and pyroarsenate for arsenic pentoxide. is currently the only formulation listed in AWPA standards. High retention levels (40 kg m–3 (2.5 lb ft–3)) of CCA CCA–C was found to have the optimum combination of preservative provide good resistance to attack by the efficacy and resistance to leaching, but the earlier formula- marine borers Limnoria and Teredo (Table 15–2). tions (CCA–A and CCA–B) have also provided long- term protection for treated stakes exposed in Mississippi Alkaline Copper Quat (ACQ) (Table 15–5). CCA–C has an actives composition of 47.5% Alkaline copper quat (ACQ) has an actives composition chromium trioxide, 34.0% arsenic pentoxide, and 18.5% of 67% copper oxide and 33% quaternary ammonium copper oxide. AWPA Standard P5 permits substitution of compound (quat). Multiple variations of ACQ have been potassium or sodium dichromate for chromium trioxide; standardized. ACQ type B (ACQ–B) is an ammoniacal cop- copper sulfate, basic copper carbonate, or copper hydroxide per formulation, ACQ type D (ACQ–D) is an amine copper formulation, and ACQ type C (ACQ–C) is a combined Table 15–2. Preservative treatment and retention ammoniacal-amine formulation with a slightly different necessary to protect round timber piles from severe quat compound. The multiple formulations of ACQ allow marine borer attacka some flexibility in achieving compatibility with a specific Retention (kg m–3)b wood species and application. When ammonia is used as the carrier, ACQ has improved ability to penetrate difficult-to- Round Sawn treat wood species. However, if the wood species is readily Marine borers and preservatives piles materials treatable, such as Southern Pine sapwood, an amine carrier Limnoria tripunctata only Ammoniacal copper zinc arsenate 40, 24c 40 can be used to provide a more uniform surface appearance. Chromated copper arsenate 40, 24c Recently ACQ has been formulated using small particles Creosote 320, 256c 400 of copper rather than copper solubilized in ethanolamine. Limnoria tripunctata and Pholads These formulations are discussed in more detail in the Pre- (dual treatment) servatives with ICC–ES Evaluation Reports section. Use of First treatment particulate copper formulations of ACQ is currently limited Ammoniacal copper zinc arsenate 16, (1.0) 24 to permeable woods (such as species of pine with a high Chromated copper arsenate 16, (1.0) 24 proportion of sapwood), but efforts continue to adapt the Second treatment Creosote 320, (20.0) 320 treatment to a broader range of wood species. Creosote solution 320, (20.0) 320 Alkaline Copper DCOI (ACD) aSee AWPA Commodity Specification G for more information. bTo convert to retention expressed as lb ft–3, divide these values by 16.0. Alkaline copper DCOI (ACD) is a recently proposed formu- cLower retention levels are for marine piling used in areas from New lation of alkaline copper ethanolamine that utilizes 4,5-di- Jersey northward on the East Coast and north of San Francisco on the chloro-2-N-octyl-4-isothiazolin-3-one (DCOI) as co-biocide West Coast in the United States.

Table 15–3. Active ingredients in waterborne preservatives used for pressure treatments Active ingredient Preservative Inorganic actives Arsenic ACZA, CCA Boron CBA–A, CX–A, SBX, KDS Chromium ACC, CCA Copper ACC, ACZA, ACQ–B, ACQ–C, ACQ–D, CA–B, CA–C, CBA–A, CCA, CXA, ESR–1721, ESR–1980, ESR–2240, ESR–2325, KDS, KDS–B, ESR–2711 Zinc ACZA Organic actives Alkylbenzyldimethyl ACQ–C ammonium compound DCOI EL2, ESR–2711 Didecyldimethyl ACQ–B, ACQ–D ammonium compound HDO: Bis-(N-cyclo- CX–A hexyldiazeniumdioxy)Cu Imdiacloprid EL2, PTI, ESR–2067 Propiconazole CA–C, PTI, ESR–1721 Polymeric betaine KDS, KDS–B Tebuconazole PTI, ESR–1721, ESR–2067, ESR–2325

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Table 15–4. Generalized examples of products that may still be treated with CCA under conditions of current label languagea 2001 AWPA Type of end use still allowed standard Lumber and timbers used in seawater C2 Land, fresh-water, and marine piles C3 Utility poles C4 Plywood C9 Wood for highway construction C14 Round, half-round, and quarter-round fence posts C16 Poles, piles, and posts used as structural members on farms C16 Members immersed in or frequently splashed by seawater C18 Lumber and plywood for permanent wood foundations C22 Round poles and posts used in building construction C23 Sawn timbers (at least 5 in. thick) used to support residential and commercial structures C24 Sawn cross-arms C25 Structural glued-laminated members C28 Structural composite lumber (parallel strand or laminated veneer lumber) C33 Shakes and shingles C34 aRefer to the EPA or a treated-wood supplier for the most recent definition of allowable uses. to provide protection against copper-tolerant fungi. The Copper HDO (CXA) ratio of alkaline copper to DCOI in the formulation ranges Copper HDO (CXA) is an amine copper water-based pre- from 20:1 to 25:1. The ACD formulation is listed as a preservative that has been used in Europe and was recently servative in AWPA standards. It has been proposed for both standardized in the United States. The active ingredients are above-ground and ground-contact applications, but at the copper oxide, boric acid, and copper–HDO (bis-(N-cyclo- time this chapter was finalized it had not yet been standard- hexyldiazeniumdioxy copper). The appearance and handling ized for treatment of any commodities. characteristics of wood treated with copper HDO are similar Copper bis(dimethyldithiocarbamate) (CDDC) to those of the other amine copper-based treatments. It is also referred to as copper xyligen. Currently, copper HDO is Copper bis(dimethyldithiocarbamate) (CDDC) is a reaction standardized only for applications that are not in direct con- product formed in wood as a result of the dual treatment of tact with soil or water. two separate treating solutions. The first treating solution contains a maximum of 5% bivalent copper–ethanolamine Copper Naphthenate (Waterborne) (2-aminoethanol), and the second treating solution con- Waterborne copper naphthenate (CuN–W) has an actives tains a minimum of 2.5% sodium dimethyldithiocarbamate composition similar to oil-borne copper naphthenate, but the (AWPA P5). Although this preservative is not currently actives are carried in a solution of ethanolamine and water commercially available, CDDC-treated wood products are instead of petroleum solvent. Wood treated with the water- included in the AWPA Commodity Standards for uses such borne formulation has a drier surface and less odor than the as residential construction. oil-borne formulation. The waterborne formulation has been Copper Azole (CA–B, CA–C and CBA–A) standardized for above-ground and some ground-contact applications (Table 15–1). Copper azole (CA–B) is a formulation composed of amine copper (96%) and tebuconazole (4%). Copper azole (CA–C) Inorganic Boron (Borax–Boric Acid) is very similar to CA–B, but half the tebuconazole is re- Borate preservatives are readily soluble in water and highly placed with propiconazole. The active ingredients in CA–C leachable and should be used only above ground where the are in the ratio of 96% amine copper, 2% tebuconazole, and wood is protected from wetting. When used above ground 2% propiconazole. An earlier formulation (CBA–A) also and protected from wetting, this preservative is very ef- contained boric acid. Although listed as an amine formula- fective against decay, termites, beetles, and carpenter ants. tion, copper azole may also be formulated with an amine– Inorganic boron (SBX) is listed in AWPA standards for ammonia formulation. The ammonia may be included when protected applications such as framing lumber. The solid or the copper azole formulations are used to treat refractory treating solution for borate preservatives (borates) should be species, and the ability of such a formulation to adequately greater than 98% pure, on an anhydrous basis (AWPA P5). treat Douglas-fir has been demonstrated. Inclusion of am- Acceptable borate compounds are sodium octaborate, so- monia, however, is likely to have slight affects on the sur- dium tetraborate, sodium pentaborate, and boric acid. These face appearance and initial odor of the treated wood. compounds are derived from the mineral sodium borate, which is the same material used in laundry additives.

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Table 15–5. Results of Forest Products Laboratory studies on 38- by 89- by 457-mm (nominal 2- by 4- by 18-in.) Southern Pine sapwood stakes, pressure-treated with commonly used wood preservatives, installed at Harrison Experimental Forest, Mississippi Average retention Average life or condition Preservative (kg m–3 (lb ft–3))a at last inspection Controls (untreated stakes) 1.8 to 3.6 years Acid copper chromate 2.08 (0.13) 11.6 years 2.24 (0.14) 6.1 years 4.01 (0.25) 80% failed after 40 years 4.17 (0.26) 80% failed after 60 years 4.65 (0.29) 4.6 years 5.93 (0.37) 60% failed after 60 years 8.01 (0.50) 50% failed after 40 years 12.18 (0.76) 22% failed after 40 years Ammoniacal copper arsenate 2.56 (0.16) 16.6 years 3.52 (0.22) 80% failed after 30 years 3.84 (0.24) 38.7 years 4.01 (0.25) 60% failed after 40 years 7.37 (0.45) 20% failed after 40 years 8.17 (0.51) 10% failed after 60 years 15.54 (0.97) No failures after 60 years 20.02 (1.25) No failures after 60 years Chromated copper arsenate 2.40 (0.15) 28.7 years Type I (Type A) 3.52 (0.22) 45% failed after 40 years 4.65 (0.29) 30% failed after 60 years 7.05 (0.44) 10% failed after 40 years 7.05 (0.44) 20% failed after 60 years Type II (Type B) 3.68 (0.23) 30% failed after 40 years 4.17 (0.26) No failures after 46 years 5.93 (0.37) No failures after 46 years 8.33 (0.52) No failures after 46 years 12.66 (0.79) No failures after 46 years 16.66 (1.04) No failures after 46 years Type III (Type C) 2.24 (0.14) No failures after 25 years 3.20 (0.20) No failures after 35 years 4.00 (0.25) 20% failed after 20 years 4.33 (0.27) 10% failed after 25 years 6.41 (0.40) No failures after 35 years 6.41 (0.40) No failures after 25 years 9.61 (0.60) No failures after 35 years 9.93 (0.62) No failures after 25 years 12.66 (0.79) No failures after 25 years Oxine copper 0.22 (0.014) 26.9 years (Copper-8-quinolinolate) 0.48 (0.03) 27.3 years AWPA P9 heavy petroleum 0.95 (0.059) 31.3 years 1.99 (0.124) No failures after 45 years Copper naphthenate 0.11% copper in No. 2 fuel oil 0.19 (0.012) 15.9 years 0.29% copper in No. 2 fuel oil 0.46 (0.029) 21.8 years 0.57% copper in No. 2 fuel oil 0.98 (0.061) 27.1 years 0.86% copper in No. 2 fuel oil 1.31 (0.082) 29.6 years Creosote, coal-tar 52.87 (3.3) 24.9 years 65.68 (4.1) 14.2 years 67.28 (4.2) 17.8 years 73.69 (4.6) 21.3 years 124.96 (7.8) 70% failed after 54-1/2 years 128.24 (8.0) 90% failed after 60 years 132.97 (8.3) 50% failed after 46 years 160.20 (10.0) 90% failed after 55 years 189.04 (11.8) 50% failed after 60 years

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In addition to pressure treatments, borates are commonly KDS sprayed, brushed, or injected to treat wood in existing KDS and KDS Type B (KDS–B) utilize copper and poly- structures. They will diffuse into wood that is wet, so these meric betaine as the primary active ingredients. The KDS preservatives are often used as a remedial treatment. Borates formulation also contains boron, and has an actives com- are widely used for log homes, natural wood finishes, and position of 41% copper oxide, 33% polymeric betaine, and hardwood pallets. 26% boric acid. KDS–B does not contain boron and has an EL2 actives composition of 56% copper oxide and 44% polymeric betaine. KDS is listed for treatment of commodities EL2 is a waterborne preservative composed of the fungicide used above ground and for general use in contact with soil 4,5-dichloro-2-N-octyl-4-isothiazolin-3-one (DCOI), the or fresh water. It is not listed for soil or fresh water contact insecticide imidacloprid, and a moisture control stabilizer in severe exposures. The listing includes treatment of (MCS). The ratio of actives is 98% DCOI and 2% imida- common pine species as well as Douglas-fir and western cloprid, but the MCS is also considered to be a necessary hemlock. KDS–B is currently in the process of obtaining component to ensure preservative efficacy. EL2 is currently listings for specific commodities. The appearance of KDS- listed in AWPA standards for above-ground applications treated wood is similar to that of wood treated with other only (Table 15–1).

15–8 Chapter 15 Wood Preservation alkaline copper formulations (light green–brown). It has Use of ESR–1721 (dispersed copper) is currently limited to some odor initially after treatment, but this odor dissipates easily treated pine species. as the wood dries. ESR–1980 Oligomeric Alkylphenol Polysulfide (PXTS) ESR–1980 includes a listing for both the AWPA standard- PXTS is a recently developed and somewhat unusual pre- ized formulation of ACQ–D and a waterborne, micronized servative system. It is an oligomer formed by the reaction of copper version of alkaline copper quat (referred to here as cresylic acid and sulfur chlorides in the presence of excess ESR–1980). The formulation is similar to ACQ in that the sulfur. PXTS is a solid at room temperature but becomes active ingredients are 67% copper oxide and 33% quater- a liquid when heated to above approximately 58 °C. It can nary ammonium compound. However, in ESR–1980 the also be dissolved and diluted in some aromatic and organic copper is ground to sub-micron dimensions and suspended chlorinated solvents. PXTS is not currently listed for treat- in the treatment solution instead of being dissolved in etha- ment of any commodities and is currently not commercially nolamine. The treated wood has little green color because available. the copper is not dissolved in the treatment solution. The use of the particulate form of copper is currently limited to Propiconazole and Tebuconazole the more easily penetrated pine species, but efforts are un- Propiconazole and tebuconazole are organic triazole bio- derway to adapt the formulation for treatment of a broader cides that are effective against wood decay fungi but not range of wood species. ESR–1980 is listed for treatment of against insects (AWPA P5, P8). They are soluble in some commodities used in both above-ground and ground-contact organic solvents but have low solubility in water and are applications. stable and leach resistant in wood. Propiconazole and tebuconazole are currently components of waterborne preserva- ESR–2067 tive treatments used for pressure-treatment of wood in the ESR–2067 is an organic waterborne preservative with an United States, Europe, and Canada. They are also used as actives composition of 98% tebuconazole (fungicide) and components of formulations used to provide mold and sap- 2% imidacloprid (insecticide). The treatment does not im- stain protection. Propiconazole is also standardized for use part any color to the wood. It is currently listed only for with AWPA P9 Type C or Type F organic solvents. treatment of commodities that are not in direct contact with soil or standing water. Propiconazole–Tebuconazole–Imidacloprid (PTI) PTI is a waterborne preservative solution composed of two ESR–2240 fungicides (propiconazole and tebuconazole) and the insec- ESR–2240 is a waterborne formulation that utilizes finely ticide imidacloprid. It is currently listed in AWPA standards ground (micronized) copper in combination with tebucon- for above-ground applications only. The efficacy of PTI is azole in an actives ratio of 25:1. It is listed for above-ground enhanced by the incorporation of a water-repellent stabilizer and ground-contact applications. In addition to wood prod- in the treatment solutions, and lower retentions are allowed ucts cut from pine species, ESR–2240 can be used for treat- with the stabilizer (Table 15–1). ment of hem–fir lumber and Douglas-fir plywood. Preservatives with ICC–ES Evaluation ESR–2325 Reports ESR–2325 is another waterborne preservative that utilizes Some commercially available waterborne wood preserva- finely ground copper particles and tebuconazole as actives. tives are not standardized by the AWPA. Instead, they have The ratio of copper to tebuconazole in the treatment solu- obtained ICC–ES evaluation reports. In this chapter we refer tion is 25:1. Its use is currently limited to more readily to these preservatives by their Evaluation Report number treated species such as the Southern Pine species group, but (Table 15–1). Douglas-fir plywood is also listed. ESR–2315 is listed for treatment of wood used above-ground and in contact with ESR–1721 soil or fresh water. ESR–1721 recognizes three preservative formulations. Two are the same formulations of copper azole (CA–B and ESR–2711 CA–C) also listed in AWPA standards. The other (referred to ESR–2711 combines copper solubilized in ethanolamine here as ESR–1721) uses particulate copper that is ground to with the fungicide 4,5-dichloro-2-N-octyl-4-isothiazolin-3- sub-micron dimensions and dispersed in the treatment solu- one (DCOI). The ratio of copper (as CuO) to DCOIT ranges tion. Wood treated with ESR–1721 has a lighter green color from 10:1 to 25:1. The ESR listing provides for both above- than the CA–B or CA–C formulations because the copper ground and ground-contact applications. The appearance of is not dissolved in the treatment solution. All three formula- the treated wood is similar to that of wood treated with other tions are listed for treatment of commodities used in a range formulations utilizing soluble copper, such as ACQ. It is of applications, including contact with soil or freshwater. currently only listed for treatment of pine species.

15–9 General Technical Report FPL–GTR–190

Oil-Borne or Oil-Type Preservatives generally more viscous than is straight creosote. High tem- Oil-type wood preservatives are some of the oldest preser- peratures and pressures during treatment, when they can be vatives, and their use continues in many applications. Wood safely used, will often improve penetration of high-viscosity does not swell from treatment with preservative oils, but it solutions. may shrink if it loses moisture during the treating process. Although coal-tar creosote or creosote solutions are well Creosote and solutions with heavy, less volatile petroleum suited for general outdoor service in structural timbers, creo- oils often help protect wood from weathering but may ad- sote has properties that are undesirable for some purposes. versely influence its cleanliness, odor, color, paintability, The color of creosote and the fact that creosote-treated wood and fire performance. Volatile oils or solvents with oil-borne usually cannot be painted satisfactorily make this preserva- preservatives, if removed after treatment, leave the wood tive unsuitable where appearance and paintability are cleaner than do the heavy oils but may not provide as much important. protection. Wood treated with some preservative oils can be glued satisfactorily, although special processing or cleaning The odor of creosote-treated wood is unpleasant to some may be required to remove surplus oils from surfaces before people. Also, creosote vapors are harmful to growing plants, spreading the adhesive. and foodstuffs that are sensitive to odors should not be stored where creosote odors are present. Workers some- Coal-Tar Creosote and Creosote Solutions times object to creosote-treated wood because it soils their Coal-tar creosote (creosote) is a black or brownish oil made clothes, and creosote vapor photosensitizes exposed skin. by distilling coal tar that is obtained after high-temperature With precautions to avoid direct skin contact with creosote, carbonization of coal. Advantages of creosote are (a) high there appears to be minimal danger to the health of workers toxicity to wood-destroying organisms; (b) relative insolu- handling or working near the treated wood. The EPA or the bility in water and low volatility, which impart to it a great wood treater should be contacted for specific information on degree of permanence under the most varied use conditions; this subject. (c) ease of application; (d) ease with which its depth of In 1986, creosote became a restricted-use pesticide, and its penetration can be determined; (e) relative low cost (when use is currently restricted to pressure-treatment facilities. purchased in wholesale quantities); and (f) lengthy record of For use and handling of creosote-treated wood, refer to the satisfactory use. Creosote is commonly used for heavy tim- EPA-approved Consumer Information Sheet. bers, poles, piles, and railroad ties. Freshly creosoted timber can be ignited and burns readily, AWPA Standard P1/P13 provides specifications for coal-tar producing a dense smoke. However, after the timber has creosote used for preservative treatment of piles, poles, and seasoned for some months, the more volatile parts of the timber for marine, land, and freshwater use. The character of oil disappear from near the surface and the creosoted wood the tar used, the method of distillation, and the temperature usually is little, if any, easier to ignite than untreated wood. range in which the creosote fraction is collected all influence Until this volatile oil has evaporated, ordinary precautions the composition of the creosote, and the composition may should be taken to prevent fires. Creosote adds fuel value, vary within the requirements of standard specifications. Un- but it does not sustain ignition. der normal conditions, requirements of these standards can be met without difficulty by most creosote producers. Other Creosotes Coal tar or petroleum oil may also be mixed with coal-tar Creosotes distilled from tars other than coal tar have been creosote, in various proportions, to lower preservative costs. used to some extent for wood preservation, although they AWPA Standard P2 provides specifications for coal-tar solu- are not included in current AWPA specifications. These tions. AWPA Standard P3 stipulates that creosote–petroleum include wood-tar creosote, oil-tar creosote, and water–gas- oil solution shall consist solely of specified proportions tar creosote. These creosotes provide some protection from of 50% coal-tar creosote by volume (which meets AWPA decay and insect attack but are generally less effective than standard P1/P13) and 50% petroleum oil by volume (which coal-tar creosote. meets AWPA standard P4). However, because no analyti- Pentachlorophenol Solutions cal standards exist to verify the compliance of P3 solutions Water-repellent solutions containing chlorinated phenols, after they have been mixed, the consumer assumes the risk principally pentachlorophenol (penta), in solvents of the of using these solutions. These creosote solutions have a mineral spirits type, were first used in commercial dip treat- satisfactory record of performance, particularly for railroad ments of wood by the millwork industry in about 1931. ties and posts where surface appearance of the treated wood Commercial pressure treatment with pentachlorophenol in is of minor importance. Compared with straight creosote, heavy petroleum oils on poles started in about 1941, and creosote solutions tend to reduce weathering and checking considerable quantities of various products soon were of the treated wood. These solutions have a greater tendency pressure treated. AWPA Standard P8 defines the properties to accumulate on the surface of the treated wood (bleed) and of pentachlorophenol preservative, stating that pentachloro- penetrate the wood with greater difficulty because they are phenol solutions for wood preservation shall contain not less

15–10 Chapter 15 Wood Preservation than 95% chlorinated phenols, as determined by titration of Water-based formulations of copper naphthenate may also hydroxyl and calculated as pentachlorophenol. be available. AWPA standard P9 defines solvents and formulations for Oxine Copper (copper-8-quinolinolate) organic preservative systems. The performance of penta- Oxine copper (copper-8-quinolinolate) is an organometalic chlorophenol and the properties of the treated wood are in- compound, and the formulation consists of at least 10% cop- fluenced by the properties of the solvent used. A commercial per-8-quinolinolate, 10% nickel-2-ethylhexanoate, and 80% process using pentachlorophenol dissolved in liquid petro- inert ingredients (AWPA P8). It is accepted as a stand-alone leum gas (LPG) was introduced in 1961, but later research preservative for aboveground use for sapstain and mold showed that field performance of penta–LPG systems was control and is also used for pressure treating (Table 15–1). inferior to penta–P9 systems. Thus, penta–LPG systems A water-soluble form can be made with dodecylbenzene are no longer used. The heavy petroleum solvent included sulfonic acid, but the solution is corrosive to metals. in AWPA P9 Type A is preferable for maximum protection, particularly when wood treated with pentachlorophenol is Oxine copper solutions are greenish brown, odorless, toxic used in contact with the ground. The heavy oils remain in to both wood decay fungi and insects, and have a low toxic- the wood for a long time and do not usually provide a clean ity to humans and animals. Because of its low toxicity to hu- or paintable surface. mans and animals, oxine copper is the only EPA-registered preservative permitted by the U.S. Food and Drug Admin- Because of the toxicity of pentachlorophenol, care is neces- istration for treatment of wood used in direct contact with sary when handling and using it to avoid excessive personal food. Some examples of its uses in wood are commercial contact with the solution or vapor. Do not use indoors or refrigeration units, fruit and vegetable baskets and boxes, where human, plant, or animal contact is likely. Pentachlo- and water tanks. Oxine copper solutions have also been used rophenol became a restricted-use pesticide in November on nonwood materials, such as webbing, cordage, cloth, 1986 and is currently only available for use in pressure leather, and plastics. treatment. For use and handling precautions, refer to the EPA-approved Consumer Information Sheet. Zinc Naphthenate Zinc naphthenate is similar to copper naphthenate but is less The results of pole service and field tests on wood treated effective in preventing decay from wood-destroying fungi with 5% pentachlorophenol in a heavy petroleum oil are and mildew. It is light colored and does not impart the char- similar to those with coal-tar creosote. This similarity has acteristic greenish color of copper naphthenate, but it does been recognized in the preservative retention requirements impart an odor. Waterborne and solventborne formulations of treatment specifications. Pentachlorophenol is effec- are available. Zinc naphthenate is not widely used for pres- tive against many organisms, such as decay fungi, molds, sure treating. stains, and insects. Because pentachlorophenol is ineffective against marine borers, it is not recommended for the treat- 3-Iodo-2-Propynyl Butyl Carbamate ment of marine piles or timbers used in coastal waters. 3-Iodo-2-propynyl butyl carbamate (IPBC) is a fungi- Copper Naphthenate cide that is used as a component of sapstain and millwork preservatives. It is also included as a fungicide in several Copper naphthenate is an organometalic compound formed surface-applied water-repellent-preservative formulations. as a reaction product of copper salts and naphthenic acids Waterborne and solvent-borne formulations are avail- that are usually obtained as byproducts in petroleum refin- able. Some formulations yield an odorless, treated product ing. It is a dark green liquid and imparts this color to the that can be painted if dried after treatment. It is listed as a wood. Weathering turns the color of the treated wood to pressure-treatment preservative in the AWPA standards but light brown after several months of exposure. The wood is not currently standardized for pressure treatment of any may vary from light brown to chocolate brown if heat is wood products. IPBC also may be combined with other used in the treating process. AWPA P8 standard defines the fungicides, such as didecyldimethylammonium chloride in properties of copper naphthenate, and AWPA P9 covers the formulations used to prevent mold and sapstain. solvents and formulations for organic preservative systems. IPBC/Permethrin Copper naphthenate is effective against wood-destroying fungi and insects. It has been used commercially since the IPBC is not an effective insecticide and has recently been 1940s and is currently standardized for a broad range of standardized for use in combination with the insecticide per- applications (Table 15–1). Copper naphthenate is not methrin (3-phenoxybenzyl-(1R,S)-cis, trans-2, 2-dimethyl- a restricted-use pesticide but should be handled as an 3-(2,2-dichlorovinyl) cycloproanecarboxylate) under the industrial pesticide. It may be used for superficial treatment, designation IPBC/PER. Permethrin is a synthetic pyrethroid such as by brushing with solutions with a copper content of widely used for insect control in agricultural and structural 1% to 2% (approximately 10% to 20% copper naphthenate). applications. The ratio of IPBC to permethrin in the IPBC/ PER varies between 1.5:1 and 2.5:1. The formulation is

15–11 General Technical Report FPL–GTR–190 carried in a light solvent such as mineral spirits, making it Zinc borate is currently listed in AWPA Commodity Stan- compatible with composite wood products that might be dard J for nonpressure treatment of laminated strand lumber, negatively affected by the swelling associated with water- oriented strandboard, and engineered wood siding. The stan- based pressure treatments. The IPBC/PER formulation is dard requires that these products have an exterior coating or intended only for use in above-ground applications. The laminate when used as siding. Another preservative that has formulation is listed as a preservative in AWPA standards, been used to protect composites is ammoniacal copper ac- but at the time this chapter was finalized it had not yet been etate, which is applied by spraying the preservative onto the standardized for treatment of any commodities. OSB flakes before drying. Alkyl Ammonium Compounds Water-Repellent and Nonpressure Alkyl ammonium compounds such as didecyldimethylam- Treatments monium chloride (DDAC) or didecyldimethylammonium Effective water-repellent preservatives will retard the in- carbonate (DDAC)/bicarbonate (DDABC) have some ef- gress of water when wood is exposed above ground. These ficacy against both wood decay fungi and insects. They are preservatives help reduce dimensional changes in the wood soluble in both organic solvents and water and are stable in as a result of moisture changes when the wood is exposed to wood as a result of chemical fixation reactions. DDAC and rainwater or dampness for short periods. As with any wood DDABC are currently being used as a component of alka- preservative, the effectiveness in protecting wood against line copper quat (ACQ) (see section on Waterborne Preser- decay and insects depends upon the retention and penetra- vatives) for above-ground and ground-contact applications tion obtained in application. These preservatives are most and as a component of formulations used for sapstain and often applied using nonpressure treatments such as vacuum mold control. impregnation, brushing, soaking, or dipping. Preservative 4,5-Dichloro-2-N-Octyl-4-Isothiazolin-3-One (DCOI) systems containing water-repellent components are sold under various trade names, principally for the dip or equivalent 4,5-dichloro-2-N-octyl-4-isothiazolin-3-one (DCOI) is a treatment of window sash and other millwork. The National biocide that is primarily effective against wood decay fungi. Wood Window and Door Association (NWWDA) standard, It is soluble in organic solvents but not in water, and it is WDMA I.S. 4–07A, Water Repellent Preservative Treatment stable and leach resistant in wood. The solvent used in the for Millwork, lists preservative formulations that have met formulation of the preservative is specified in AWPA P9 certain requirements, including EPA registration and effi- Type C. DCOI can be formulated to be carried in a water- cacy against decay fungi. borne system, and it is currently used as a component in the waterborne preservative EL2. It has also recently been The AWPA Commodity Specification I for nonpressure proposed for use as co-biocide in a copper ethanolamine treatment of millwork and other wood products provides re- formulation referred to as ACD. quirements for these nonpressure preservatives but does not currently list any formulations. The preservative must also Chlorpyrifos meet the Guidelines for Evaluating New Wood Preservatives Chlorpyrifos (CPF) is an organophosphate insecticide that for Consideration by the AWPA for nonpressure treatment. has been widely used for agricultural purposes. It has been standardized by the AWPA as a preservative but is not cur- Water-repellent preservatives containing oxine copper are rently used as a component of commercial pressure treat- used in nonpressure treatment of wood containers, pallets, ments. Chloropyrifos is not effective in preventing fungal and other products for use in contact with foods. When attack and should be combined with an appropriate fungi- combined with volatile solvents, oxine copper is used to cidal preservative for most applications. pressure-treat lumber intended for use in decking of trucks and cars or related uses involving harvesting, storage, and Treatments for Wood Composites transportation of foods (AWPA P8). Many structural composite wood products, such as glued- Nonpressure preservatives sold to consumers for household laminated beams, plywood, and parallel strand and lami- and farm use typically contain copper naphthentate, zinc nated veneer lumber, can be pressure-treated with wood pre- naphthenate, or oxine copper. Their formulations may also servatives in a manner similar to lumber. However, flake- or incorporate water repellents. fiber-based composites are often protected by adding preservative during manufacture. A commonly used preservative Selecting Preservatives for these types of composites is zinc borate. Zinc borate is a white, odorless powder with low water solubility that is The type of preservative applied is often dependent on the added directly to the furnish or wax during panel manufac- requirements of the specific application. For example, direct ture. Zinc borate has greater leach resistance than the more contact with soil or water is considered a severe deteriora- soluble forms of borate used for pressure treatment and tion hazard, and preservatives used in these applications thus can be used to treat composite siding products that are must have a high degree of leach resistance and efficacy exposed outdoors but partially protected from the weather. against a broad spectrum of organisms. These same

15–12 Chapter 15 Wood Preservation

evaluating wood treatments requires numerous tests. Some of the most important tests are mentioned here, but they should be considered only as a minimum, and other tests are useful as well. Appendix A of the AWPA Standards provides detailed guidelines on the types of tests that may be needed to evaluate new wood preservatives. The laboratory leaching test helps to evaluate how rapidly the treatment will be depleted. A treatment needs leach resistance to provide long-term protection. In this test small cubes of wood are immersed in water for 2 weeks. The laboratory decay test is used to challenge the treated wood with certain fungal isolates that are known to aggres- sively degrade wood. It should be conducted with specimens Figure 15–1. Field stake test plot at Harrison Experi- that have been through the leaching test. The extent of decay mental Forest in southern Mississippi. in wood treated with the test preservative is compared to that of untreated wood and wood treated with an established preservatives may also be used at lower retentions to protect preservative. This test can help to determine the treatment wood exposed in lower deterioration hazards, such as above level needed to prevent decay. the ground. The exposure is less severe for wood that is par- Field stake evaluations are some of the most informative tially protected from the weather, and preservatives that lack tests because they challenge the treated wood with a the permanence or toxicity to withstand continued exposure wide range of natural organisms under severe conditions to precipitation may be effective in those applications. Other (Fig. 15–1). Stakes are placed into the soil in regions with formulations may be so readily leachable that they can be a warm, wet climate (usually either the southeastern United used only indoors. States or Hawaii). At least two different sites are used to To guide selection of the types of preservatives and loadings account for differences in soil properties and types of organ- appropriate to a specific end use, the AWPA recently devel- isms present. The extent of deterioration in wood treated oped use category system (UCS) standards. The UCS stan- with the test preservative is compared to that of untreated dards simplify the process of finding appropriate preserva- wood and wood treated with an established preservative. tives and preservative retentions for specific end uses. They Above-ground field exposures are useful for treatments that categorize treated wood applications by the severity of the will be used to protect wood above ground. Although not deterioration hazard (Table 15–6). The lowest category, Use as severe as field stake tests, above-ground tests do provide Category 1 (UC1), is for wood that is used in interior con- useful information on above-ground durability. Specimens struction and kept dry; UC2 is for interior wood completely are exposed to the weather in an area with a warm, wet protected from the weather but occasionally damp. UC3 is climate (usually either the southeastern United States or for exterior wood used above ground; UC4 is for wood used Hawaii). The specimens are designed to trap moisture and in ground contact in exterior applications. UC5 includes ap- create ideal conditions for above-ground decay. The extent plications that place treated wood in contact with seawater of deterioration in wood treated with the test preservative is and marine borers. Individual commodity specifications then compared to that of untreated wood and wood treated with list all the preservatives that are standardized for a specific an established preservative. use category along with the appropriate preservative retention. Corrosion testing is used to determine the compatibility of the treatment with metal fasteners. Although some preservatives are effective in almost all environments, they may not be well-suited for applications Treatability testing is used to evaluate the ability of a treat- involving frequent human contact or for exposures that ment to penetrate deeply into the wood. Shallow surface present only low to moderate biodeterioration hazards. Ad- treatments rarely provide long-term protection because ditional considerations include cost, potential odor, surface degrading organisms can still attack the interior of the wood. dryness, adhesive bonding, and ease of finish application. Strength testing compares the mechanical properties of treated wood with matched, untreated specimens. Treatment Evaluating New Preservatives chemicals or processes have the potential to damage the Wood preservatives often need to provide protection from a wood, making it weak or brittle. wide range of wood-attacking organisms (fungi, insects, marine borers, and bacteria). Because they must protect wood Preservative Effectiveness in so many ways, and protect wood for a long time period, Preservative effectiveness is influenced not only by the protective value of the preservative chemical, but also by the

15–13 General Technical Report FPL–GTR–190

Table 15–6. Summary of use category system developed by the American Wood Protection Association Common agents of Use category Service conditions Use environment deterioration Typical applications UC1 Interior construction Continuously protected Insects only Interior construction and Above ground from weather or other furnishings Dry sources of moisture UC2 Interior construction Protected from weather, but Decay fungi and insects Interior construction Above ground may be subject to sources Damp of moisture UC3A Exterior construction Exposed to all weather Decay fungi and insects Coated millwork, siding, Above ground cycles, not exposed to and trim Coated and rapid water prolonged wetting runoff UC3B Ground contact or fresh Exposed to all weather Decay fungi and insects Fence, deck, and water cycles, normal exposure guardrail posts, crossties Non-critical components conditions and utility poles (low decay areas) UC4A Ground contact or fresh Exposed to all weather Decay fungi and insects Fence, deck, and water cycles, normal exposure guardrail posts, crossties Non-critical components conditions and utility poles (low decay areas) UC4B Ground contact or fresh Exposed to all weather Decay fungi and insects Permanent wood water cycles, high decay potential with increased potential foundations, building Critical components or includes salt-water splash for biodeterioration poles, horticultural difficult replacement posts, crossties and utility poles (high decay areas) UC4C Ground contact or fresh Exposed to all weather Decay fungi and insects Land and fresh-water water cycles, severe environments, with extreme potential piling, foundation piling, Critical structural extreme decay potential for biodeterioration crossties and utility components poles (severe decay areas) UC5A Salt or brackish water Continuous marine exposure Salt-water organisms Piling, bulkheads, and adjacent mud zone (salt water) bracing Northern waters UC5B Salt or brackish water Continuous marine exposure Salt-water organisms, Piling, bulkheads, and adjacent mud zone (salt water) including bracing NJ to GA, south of San creosote-tolerant Francisco Limnoria tripunctata UC5C Salt or brackish water and Continuous marine exposure Salt-water organisms, Piling, bulkheads, adjacent mud zone (salt water) including Martesia, bracing South of GA, Gulf Coast, Sphaeroma Hawaii, and Puerto Rico

method of application and extent of penetration and reten- Few service tests include a variety of preservatives under tion of the preservative in the treated wood. Even with an comparable conditions of exposure. Furthermore, service effective preservative, good protection cannot be expected tests may not show a good comparison between different with poor penetration or substandard retention levels. The preservatives as a result of the difficulty in controlling for species of wood, proportion of heartwood and sapwood, differences in treatment quality. Comparative data under heartwood penetrability, and moisture content are among the similar exposure conditions, with various preservatives and important variables that influence the results of treatment. retention levels, are included in the U.S. Forest Service, For- For various wood products, the preservatives and retention est Products Laboratory, stake test studies. A summary of levels listed in the AWPA Commodity Standards or ICC–ES these test results is included in Table 15–5. Note, however, evaluation reports are given in Table 15–1. that because the stakes used in these studies are treated under carefully controlled conditions, their performance may Determining whether one preservative is more effective not reflect variability in performance exhibited by a broad than another within a given use category is often difficult. range of commercially treated material.

15–14 Chapter 15 Wood Preservation

western larch, Sitka spruce, western hemlock, western redcedar, northern white-cedar, and white fir (A. concolor). Ex- amples of species with sapwood and heartwood somewhat resistant to penetration are the red and white spruces and Rocky Mountain Douglas-fir. Cedar poles are commonly incised to obtain satisfactory preservative penetration. With round members, such as poles, posts, and piles, the penetration of the sapwood is important in achieving a protective outer zone around the heartwood. The proportion of sapwood varies greatly with wood spe- Figure 15–2. During pressure treatment, preservative cies, and this becomes an important factor in obtaining ad- typically penetrates only the sapwood. Round mem- equate penetration. Species within the Southern Pine group bers have a uniform treated sapwood shell, but sawn are characterized by a large sapwood zone that is readily members may have less penetration on one or more penetrated by most types of preservatives. In part because faces. of their large proportion of treatable sapwood, these pine species are used for the vast majority of treated products Similar comparisons have been conducted for preservative in the United States. Other important lumber species, such treatments of small wood panels in marine exposure (Key as Douglas-fir, have a narrower sapwood band in the living West, Florida). These preservatives and treatments include tree, and as a result products manufactured from Douglas-fir creosotes with and without supplements, waterborne pre- have a lower proportion of treatable sapwood. servatives, waterborne preservative and creosote dual treatments, chemical modifications of wood, and various chemi- The heartwood of most species is difficult to treat. There cally modified polymers. In this study, untreated panels were may be variations in the resistance to preservative penetra- badly damaged by marine borers after 6 to 18 months of tion of different wood species. Table 15–7 gives the relative exposure, whereas some treated panels have remained free resistance of the heartwood to treatment of various soft- of attack after 19 years in the sea. wood and hardwood species. Although less treatable than sapwood, well-dried white fir, western hemlock, northern Test results based on seawater exposure have shown that red oak, the ashes, and tupelo are examples of species with dual treatment (waterborne copper-containing preservatives heartwood that is reasonably easy to penetrate. The southern followed by creosote) is possibly the most effective method pines, ponderosa pine, redwood, Sitka spruce, coastal Doug- of protecting wood against all types of marine borers. The las-fir, beech, maples, and birches are examples of species AWPA standards have recognized this process as well as the with heartwood that is moderately resistant to penetration. treatment of marine piles with high retention levels of ammoniacal copper zinc arsenate (ACZA) or chromated copper Preparation of Wood for Treatment arsenate (CCA). The recommended treatment and retention For satisfactory treatment and good performance, the wood in kilograms per cubic meter (pounds per cubic foot) for product must be sound and suitably prepared. Except in spe- round timber piles exposed to severe marine borer hazard cialized treating methods involving unpeeled or green mate- are given in Table 15–2. Poorly treated or untreated heart- rial, the wood should be well peeled and either seasoned or wood faces of wood species containing “high sapwood” that conditioned in the cylinder before treatment. It is also highly do not require heartwood penetration (for example, southern desirable that all machining be completed before treatment, pines, ponderosa pine, and red pine) have been found to including incising (to improve the preservative penetration perform inadequately in marine exposure. In marine appli- in woods that are resistant to treatment) and the operations cations, only sapwood faces should be allowed for water- of cutting or boring of holes. borne-preservative-treated pine in direct seawater exposure. Peeling Effect of Species on Penetration Peeling round or slabbed products is necessary to enable the The effectiveness of preservative treatment is influenced by wood to dry quickly enough to avoid decay and insect dam- the penetration and distribution of the preservative in the age and to permit the preservative to penetrate satisfactorily. wood. For maximum protection, it is desirable to select Even strips of the thin inner bark may prevent penetration. species for which good penetration is assured. Patches of bark left on during treatment usually fall off in time and expose untreated wood, thus permitting decay to In general, the sapwood of most softwood species is not dif- reach the interior of the member. ficult to treat under pressure (Fig. 15–2). Examples of species with sapwood that is easily penetrated when it is well Careful peeling is especially important for wood that is to dried and pressure treated are the pines, coastal Douglas-fir, be treated by a nonpressure method. In the more thorough

15–15 General Technical Report FPL–GTR–190

Table 15–7. Penetration of the heartwood of various softwood and hardwood speciesa Ease of treatment Softwoods Hardwoods Least difficult Bristlecone pine (Pinus aristata) American basswood (Tilia americana) Pinyon (P. edulis) Beech (white heartwood) (Fagus grandifolia) Pondersosa pine (P. pondersosa) Black tupelo (blackgum) (Nyssa sylvatica) Redwood (Sequoia sempervirens) Green ash (Fraxinus pennsylvanica var. lanceolata) Pin cherry (Prunus pennsylvanica) River birch (Betula nigra) Red oak (Quercus spp.) Slippery elm (Ulmus fulva) Sweet birch (Betula lenia) Water tupelo (Nyssa aquatica) White ash (Fraxinus americana) Moderately Baldcypress (Taxodium distichum) Black willow (Salix nigra) difficult California red fir (Abies magnifica) Chestnut oak (Quercus montana) Douglas-fir (coast) (Pseudotsuga taxifolia)) Cottonwood (Populus sp.) Eastern white pine (Pinus strobus) Bigtooth aspen (P. grandidentata) Jack pine (P. banksiana) Mockernut hickory (Carya tomentosa) Loblolly pine (P. taeda) Silver maple (Acer saccharinum) Longleaf pine (P. palustris) Sugar maple (A. saccharum) Red pine (P. resinosa) Yellow birch (Betula lutea) Shortleaf pine (P. echinata) Sugar pine (P. lambertiana) Western hemlock (Tsuga heterophylla) Difficult Eastern hemlock (Tsuga canadensis) American sycamore (Platanus occidentalis) Engelmann spruce (Picea engelmanni) Hackberry (Celtis occidentalis) Grand fir (Abies grandis) Rock elm (Ulmus thomoasi) Lodgepole pine (Pinus contorta var. latifolia) Yellow-poplar (Liriodendron tulipifera) Noble fir (Abies procera) Sitka spruce (Picea sitchensis) Western larch (Larix occidentalis) White fir (Abies concolor) White spruce (Picea glauca) Very difficult Alpine fir (Abies lasiocarpa) American beech (red heartwood) (Fagus grandifolia) Corkbark fir (A. lasiocarpa var. arizonica) American chestnut (Castanea dentata) Douglas-fir (Rocky Mountain) (Pseudotsuga taxifolia) Black locust (Robinia pseudoacacia) Northern white-cedar (Thuja occidentalis) Blackjack oak (Quercus marilandica) Tamarack (Larix laricina) Sweetgum (redgum) (Liquidambar styraciflua) Western redcedar (Thuja plicata) White oak (Quercus spp.) aAs covered in MacLean (1952). processes, some penetration may take place both longitu- opening after treatment and exposing unpenetrated wood. dinally and tangentially in the wood; consequently, small Good penetration of heated organic-based preservatives may strips of bark are tolerated in some specifications. Processes be possible in wood with a moisture content as high as 40% in which a preservative is forced or permitted to diffuse to 60%, but severe checking while drying after treatment through green wood lengthwise do not require peeling of the can expose untreated wood. timber. Machines of various types have been developed for peeling round timbers, such as poles, piles, and posts (Fig. For large timbers and railroad ties, air drying is a widely 15–3). used method of conditioning. Despite the increased time, labor, and storage space required, air drying is generally the Drying most inexpensive and effective method, even for pressure Drying of wood before treatment is necessary to prevent treatment. However, wet, warm climatic conditions make it decay and stain and to obtain preservative penetration. difficult to air dry wood adequately without objectionable However, for treatment with waterborne preservatives by infection by stain, mold, and decay fungi. Such infected certain diffusion methods, high moisture content levels may wood is often highly permeable; in rainy weather, infected be permitted. For treatment by other methods, however, dry- wood can absorb a large quantity of water, which prevents ing before treatment is essential. Drying before treatment satisfactory treatment. opens up the checks before the preservative is applied, thus How long the timber must be air dried before treatment increasing penetration, and reduces the risk of checks depends on the climate, location, and condition of the

15–16 Chapter 15 Wood Preservation

Lumber of all species, including Southern Pine poles, is often kiln dried before treatment, particularly in the southern United States where proper air seasoning is difficult. Kiln drying has the important added advantage of quickly reducing moisture content, thereby reducing transportation charges on poles. Conditioning of Green Products Plants that treat wood by pressure processes can condition green material by means other than air and kiln drying. Thus, they avoid a long delay and possible deterioration of the timber before treatment. Figure 15–3. Machine peeling of poles. The outer bark has been removed by hand, and the inner bark is being When green wood is to be treated under pressure, one of peeled by machine. Frequently, all the bark is removed several methods for conditioning may be selected. The by machine. steaming-and-vacuum process is used mainly for southern pines, and the Boulton or boiling-under-vacuum process is used for Douglas-fir and sometimes hardwoods. In the steaming process, the green wood is steamed in the treating cylinder for several hours, usually at a maximum of 118 °C (245 °F). When steaming is completed, a vacuum is immediately applied. During the steaming period, the outer part of the wood is heated to a temperature approaching that of the steam; the subsequent vacuum lowers the boiling point so that part of the water is evaporated or forced out of the wood by the steam produced when the vacuum is applied. The steaming and vacuum periods used depend upon the wood size, species, and moisture content. Steaming and vacuum usually reduce the moisture content of green wood slightly, and the heating assists greatly in getting the preservative to penetrate. A sufficiently long steaming period will also sterilize the wood. In the Boulton or boiling-under-vacuum method of partial seasoning, the wood is heated in the oil preservative under vacuum, usually at about 82 to 104 °C (180 to 220 °F). This temperature range, lower than that of the steaming process, is a considerable advantage in treating woods that are especially susceptible to injury from high temperatures. The Figure 15–4. Deep incising permits better penetration of preservative. Boulton method removes much less moisture from heartwood than from sapwood. Incising seasoning yard, methods of piling, season of the year, timber size, and species. The most satisfactory seasoning practice Wood that is resistant to penetration by preservatives may for any specific case will depend on the individual drying be incised before treatment to permit deeper and more uni- conditions and the preservative treatment to be used. There- form penetration. To incise, lumber and timbers are passed fore, treating specifications are not always specific as to through rollers equipped with teeth that sink into the wood moisture content requirements. to a predetermined depth, usually 13 to 19 mm (1/2 to 3/4 in.). The teeth are spaced to give the desired distribution To prevent decay and other forms of fungal infection during of preservative with the minimum number of incisions. A air drying, the wood should be cut and dried when condi- machine of different design is required for deeply incising tions are less favorable for fungus development (Chap. 14). the butts of poles, usually to a depth of 64 mm (2.5 in.) If this is impossible, chances for infection can be minimized (Fig. 15–4). by prompt conditioning of the green material, careful piling and roofing during air drying, and pretreating the green Incising is effective because preservatives usually penetrate wood with preservatives to protect it during air drying. the wood much farther along the grain than across the grain. The incisions open cell lumens along the grain, which

15–17 General Technical Report FPL–GTR–190 greatly enhances penetration. Incising is especially effective standard procedure for timbers to be treated with creosote in improving penetration in the heartwood areas of sawn when protection against marine borers is required. Water- surfaces. borne preservatives may be applied by the full-cell process if uniformity of penetration and retention is the primary con- Incising is practiced primarily on Douglas-fir, western hem- cern. With waterborne preservatives, control over preserva- lock, and western larch ties and timbers for pressure treat- tive retention is obtained by regulating the concentration of ment and on cedar and Douglas-fir poles. Incising can result the treating solution. in significant reductions in strength (Chap. 5). Steps in the full-cell process are essentially the following: Cutting and Framing All cutting and boring of holes should be done prior to pre- 1. The charge of wood is sealed in the treating cylinder, servative treatment. Cutting into the wood in any way after and a preliminary vacuum is applied for a half-hour or treatment will frequently expose the untreated interior of the more to remove the air from the cylinder and as much timber and permit ready access to decay fungi or insects. as possible from the wood. 2. The preservative, at ambient or elevated temperature In some cases, wood structures can be designed so that depending on the system, is admitted to the cylinder all cutting and framing is done before treatment. Railroad without breaking the vacuum. companies have followed this practice and have found it not only practical but economical. Many wood-preserving 3. After the cylinder is filled, pressure is applied until the plants are equipped to carry on such operations as the adz- wood will take no more preservative or until the re- ing and boring of crossties; gaining, roofing, and boring of quired retention of preservative is obtained. poles; and framing of material for bridges and specialized 4. When the pressure period is completed, the preservative structures, such as water tanks and barges. is withdrawn from the cylinder. Treatment of the wood with preservative oils results in little 5. A short final vacuum may be applied to free the charge or no dimensional change. With waterborne preservatives, from dripping preservative. however, some change in the size and shape of the wood When the wood is steamed before treatment, the preserva- may occur even though the wood is redried to the moisture tive is admitted at the end of the vacuum period that follows content it had before treatment. If precision fitting is nec- steaming. When the timber has received preliminary condi- essary, the wood is cut and framed before treatment to its tioning by the Boulton or boiling-under-vacuum process, the approximate final dimensions to allow for slight surfacing, cylinder can be filled and the pressure applied as soon as the trimming, and reaming of bolt holes. Grooves and bolt holes conditioning period is completed. for timber connectors are cut before treatment and can be reamed out if necessary after treatment. Modified Full Cell The modified full-cell process is basically the same as the Application of Preservatives full-cell process except for the amount of initial vacuum and the occasional use of an extended final vacuum. The modi- Wood-preserving methods are of two general types: (a) pres- fied full-cell process uses lower levels of initial vacuum; the sure processes, in which the wood is impregnated in closed actual amount is determined by the wood species, material vessels under pressures considerably above atmospheric, size, and final retention desired. The modified full-cell pro- and (b) nonpressure processes, which vary widely in the cess is commonly used for treatment of lumber with water- procedures and equipment used. borne preservatives. Pressure Processes Empty Cell In commercial practice, wood is most often treated by im- The objective of the empty-cell process is to obtain deep mersing it in a preservative in a high-pressure apparatus and penetration with a relatively low net retention of preserva- applying pressure to drive the preservative into the wood. tive. For treatment with oil preservatives, the empty-cell Pressure processes differ in details, but the general principle process should always be used if it will provide the desired is the same. The wood, on cars or trams, is run into a long retention. Two empty-cell processes, the Rueping and the steel cylinder, which is then closed and filled with preserva- Lowry, are commonly employed; both use the expansive tive (Fig. 15–5). Pressure forces the preservative into the force of compressed air to drive out part of the preservative wood until the desired amount has been absorbed. Consider- absorbed during the pressure period. able preservative is absorbed, with relatively deep penetration. Three pressure processes are commonly used: full cell, The Rueping empty-cell process, often called the empty-cell modified full cell, and empty cell. process with initial air, has been widely used for many years in Europe and the United States. The following general pro- Full Cell cedure is employed: The full-cell (Bethel) process is used when the retention of a maximum quantity of preservative is desired. It is a

15–18 Chapter 15 Wood Preservation

Figure 15–5. Typical steps in pressure treating process: A, untreated wood is placed in cylinder; B, a vacuum is applied to pull air out of the wood; C, the wood is immersed in solution while still under vacuum; D, pressure is applied to force the preservative into the wood; E, preservative is pumped out, and a final vacuum is pulled to remove excess preservative; F, excess preservative is pumped away, and the wood is removed from the cylinder.

1. Air under pressure is forced into the treating cylinder, 2. After the period of preliminary air pressure, preserva- which contains the charge of wood. The air penetrates tive is forced into the cylinder. As the preservative is some species easily, requiring but a few minutes appli- pumped in, the air escapes from the treating cylinder cation of pressure. In treating the more resistant species, into an equalizing or Rueping tank, at a rate that keeps common practice is to maintain air pressure from the pressure constant within the cylinder. When the 1/2 to 1 h before admitting the preservative, but the treating cylinder is filled with preservative, the treating necessity for lengthy air-pressure periods does not seem pressure is increased above that of the initial air and is fully established. The air pressures employed generally maintained until the wood will absorb no more preser- range from 172 to 689 kPa (25 to 100 lb in–2), depend- vative, or until enough has been absorbed to leave the ing on the net retention of preservative desired and the required retention of preservative in the wood after the resistance of the wood. treatment.

15–19 General Technical Report FPL–GTR–190

3. At the end of the pressure period, the preservative is Chemicals commonly used in waterborne salt preservatives, drained from the cylinder, and surplus preservative including chromium, copper, arsenic, and ammonia, are is removed from the wood with a final vacuum. The reactive with wood. Thus, these chemicals are potentially amount of preservative recovered can be from 20% to damaging to mechanical properties and may also promote 60% of the gross amount injected. corrosion of mechanical fasteners. The Lowry is often called the empty-cell process without Significant reductions in mechanical properties may be ob- initial air pressure. Preservative is admitted to the cylinder served if the treating and subsequent drying processes are without either an initial air pressure or a vacuum, and the air not controlled within acceptable limits. Factors that influ- originally in the wood at atmospheric pressure is imprisoned ence the effect of the treating process on strength include during the filling period. After the cylinder is filled with the (a) species of wood, (b) size and moisture content of the preservative, pressure is applied, and the remainder of timbers treated, (c) type and temperature of heating medium, the treatment is the same as described for the Rueping (d) length of the heating period in conditioning the wood for treatment. treatment and time the wood is in the hot preservative, (e) post-treatment drying temperatures, and (f) amount of The Lowry process has the advantage that equipment for the pressure used. Most important of those factors are the sever- full-cell process can be used without other accessories that ity and duration of the in-retort heating or post-treatment the Rueping process usually requires, such as an air com- redrying conditions used. The effect of wood preservatives pressor, an extra cylinder or Rueping tank for the preserva- on the mechanical properties of wood is covered in tive, or a suitable pump to force the preservative into the Chapter 5. cylinder against the air pressure. However, both processes have advantages and are widely and successfully used. Nonpressure Processes With poles and other products where bleeding of preserva- The numerous nonpressure processes differ widely in the tive oil is objectionable, the empty-cell process is followed penetration and retention levels of preservative attained, and by either heating in the preservative (expansion bath) at a consequently in the degree of protection they provide to the maximum of 104 °C (220 °F) or a final steaming for a speci- treated wood. When similar retention and penetration levels fied time limit at a maximum of 116 °C (240 °F) prior to the are achieved, wood treated by a nonpressure method should final vacuum. have a service life comparable to that of wood treated by pressure. Nevertheless, results of nonpressure treatments, Treating Pressures and Preservative Temperatures particularly those involving surface applications, are not The pressures used in treatments vary from about 345 to generally as satisfactory as those of pressure treatment. The 1,723 kPa (50 to 250 lb in–2), depending on the species and superficial processes do serve a useful purpose when more the ease with which the wood takes the treatment. Most thorough treatments are impractical or exposure conditions commonly, pressures range from about 862 to 1,207 kPa are such that little preservative protection is required. (125 to 175 lb in–2). Many woods are sensitive to high treating pressures, especially when hot. For example, Nonpressure methods, in general, consist of (a) surface AWPA standards permit a maximum pressure of 1,050 kPa application of preservatives by brief dipping, (b) soaking (150 lb in–2) in the treatment of redwood, eastern hemlock, in preservative oils or steeping in solutions of waterborne and eastern white pine, while the limitation for oak is preservatives, (c) diffusion processes with waterborne pre- 1,723 kPa (250 lb in–2). servatives, (d) vacuum treatment, and (e) a variety of miscellaneous processes. AWPA T1 standard requires that the temperature of creosote and creosote solutions, as well as that of the oil-type Brief Dipping preservatives, during the pressure period not be greater It is a common practice to treat window sash, frames, and than 100 °C (212 °F). For the waterborne preservatives that other millwork, either before or after assembly, by dipping contain chromium (ACC and CCA), the maximum solution the item in a water-repellent preservative. temperature is limited to 50 °C (120 °F) to avoid premature In some cases, preservative oil penetrates the end surfaces precipitation of the preservative. For most other waterborne of ponderosa pine sapwood as much as 25 to 76 mm preservatives, the maximum solution temperature is 65 °C (1 to 3 in.). However, end penetration in such woods as the (150 °F), although a higher limit 93 °C (200 °F) is permitted heartwood of southern pines and Douglas-fir is much less. for inorganic boron solutions. Transverse penetration of the preservative applied by brief Effect on Mechanical Properties dipping is very shallow, usually less than a millimeter (a few hundredths of an inch). The exposed end surfaces at joints Coal-tar creosote, creosote solutions, and pentachlorophenol are the most vulnerable to decay in millwork products; dissolved in petroleum oils are practically inert to wood and therefore, good end penetration is especially advantageous. have no chemical influence that would affect its strength. Dip applications provide very limited protection to wood

15–20 Chapter 15 Wood Preservation used in contact with the ground or under very moist condi- Vacuum Process tions, and they provide very limited protection against attack The vacuum process, or “VAC–VAC” as referred to in Eu- by termites. However, they do have value for exterior wood- rope, has been used to treat millwork with water-repellent work and millwork that is painted, not in contact with the preservatives and construction lumber with waterborne and ground, and exposed to moisture only for brief periods. water-repellent preservatives. Cold Soaking and Steeping In treating millwork, the objective is to use a limited quan- The methods of cold soaking well-seasoned wood for sever- tity of water-repellent preservative and obtain retention al hours or days in low-viscosity preservative oils or steep- and penetration levels similar to those obtained by dipping ing green or seasoned wood for several days in waterborne for 3 min. In this treatment, a quick, low initial vacuum is preservatives have provided a range of success on fence followed by filling the cylinder under vacuum, releasing posts, lumber, and timbers. the vacuum and soaking, followed by a final vacuum. This treatment provides better penetration and retention than the Pine posts treated by cold soaking for 24 to 48 h or longer in 3-min dip treatment, and the surface of the wood is quickly a solution containing 5% of pentachlorophenol in No. 2 fuel dried, thus expediting glazing, priming, and painting. The oil have shown an average life of 16 to 20 years or longer. vacuum treatment is also reported to be less likely than dip The sapwood in these posts was well penetrated, and preser- treatment to leave objectionably high retention levels in vative solution retention levels ranged from 32 to 96 kg m–3 bacteria-infected wood referred to as “sinker stock.” (2 to 6 lb in–3). Most species do not treat as satisfactorily as do the pines by cold soaking, and test posts of such woods Lumber intended for buildings has been treated by the as birch, aspen, and sweetgum treated by this method have vacuum process, either with a waterborne preservative or failed in much shorter times. a water-repellent/preservative solution, with preservative retention levels usually less than those required for pressure Preservative penetration and retention levels obtained by treatment. The process differs from that used in treating cold soaking lumber for several hours are considerably bet- millwork in employing a higher initial vacuum and a longer ter than those obtained by brief dipping of similar species. immersion or soaking period. However, preservative retention levels seldom equal those obtained in pressure treatment except in cases such as sap- In a study by the Forest Products Laboratory, an initial wood of pines that has become highly absorptive through vacuum of -93 kPa (27.5 inHg) was applied for 30 min, fol- mold and stain infection. lowed by a soaking for 8 h, and a final or recovery vacuum of -93 kPa (27.5 inHg) for 2 h. Results of the study showed Steeping with waterborne preservatives has very limited use good penetration of preservative in the sapwood of dry in the United States but it has been used for many years in lumber of easily penetrated species such as the pines. How- Europe. In treating seasoned wood, both the water and the ever, in heartwood and unseasoned sapwood of pine and preservative salt in the solution soak into the wood. With heartwood of seasoned and unseasoned coastal Douglas-fir, green wood, the preservative enters the water-saturated penetration was much less than that obtained by pressure wood by diffusion. Preservative retention and penetration treatment. Preservative retention was less controllable in levels vary over a wide range, and the process is not vacuum than in empty-cell pressure treatment. Good control generally recommended when more reliable treatments over retention levels is possible in vacuum treatment with are practical. a waterborne preservative by adjusting concentration of the Diffusion Processes treating solution. In addition to the steeping process, diffusion processes are Miscellaneous Nonpressure Processes used with green or wet wood. These processes employ Several other nonpressure methods of various types have waterborne preservatives that will diffuse out of the water of been used to a limited extent. Many of these involve the the treating solution or paste into the water of the wood. application of waterborne preservatives to living trees. The The double-diffusion process developed by the Forest Prod- Boucherie process for the treatment of green, unpeeled ucts Laboratory has shown very good results in fence post poles has been used for many years in Europe. This process tests and standard 38- by 89-mm (nominal 2- by 4-in.) stake involves attaching liquid-tight caps to the butt ends of the tests, particularly for full-length immersion treatments. This poles. Then, through a pipeline or hose leading to the cap, a process consists of steeping green or partially seasoned waterborne preservative is forced under hydrostatic pressure wood first in one chemical solution, then in another. The into the pole. two chemicals then react in the wood to form a precipitate A tire-tube process is a simple adaptation of the Boucherie with low solubility. However, the preservatives evaluated in process used for treating green, unpeeled fence posts. In this process do not currently have EPA registration for use in this treatment, a section of used inner tube is fastened tight nonpressure treatments. around the butt end of the post to make a bag that holds a

15–21 General Technical Report FPL–GTR–190 solution of waterborne preservative. There are now limita- subsequent precipitation. Borates are sold either as concen- tions for application of these processes because of the poten- trated liquids (typically formulated with glycol) or as pow- tial loss of preservative to the soil around the treatment site. ders that can be diluted with water. In-Place and Remedial Treatments Another type of surface treatment is the application of wa- In-place treatments may be beneficial both during construc- ter-soluble pastes containing combinations of copper naph- tion and as part of an inspection and maintenance program. thenate, copper quinolinolate, copper hydroxide, or borates. Although cutting or drilling pressure-treated wood during The theory with these treatments is that the diffusible com- construction is undesirable, it cannot always be avoided. ponents (such as boron) will move through the wood, while When cutting is necessary, the damage can be partly over- the copper component remains near the surface of a void or come by a thorough application of copper naphthenate (1% check. These pastes are most commonly used to help protect to 2% copper) to the cut surface. This provides a protective the ground-line area of poles. After the paste is applied, it is coating of preservative on the surface that may slowly mi- a covered with a wrap to hold the paste against the pole and grate into the end grain of the wood. The exposed end-grain prevent loss into the soil. In bridge piles this type of paste in joints, which is more susceptible to moisture absorption, application should be limited to terrestrial piles that will and the immediate area around all fasteners, including drill not be continually or frequently exposed to standing water. holes, will require supplemental on-site treatment. A special These pastes may also be effective if used under cap beams device is available for pressure-treating bolt holes that are or covers to protect exposed end-grain. Reapplication sched- bored after treatment. For treating the end surfaces of piles ules will vary based on the manufacturers recommendations where they are cut off after driving, at least two generous as well as the method and area of application. coats of copper naphthenate should be applied. A coat of as- Internal Diffusible Treatments phalt or similar material may be thoroughly applied over the Surface-applied treatments often do not penetrate deeply copper naphthenate, followed by some protective sheet ma- enough to protect the inner portions of large wooden mem- terial, such as metal, roofing felt, or saturated fabric, fitted bers. An alternative to surface-applied treatments is instal- over the pile head and brought down the sides far enough to lation of internal diffusible chemicals. These diffusible protect against damage to the treatment and against the en- treatments are available in liquid, solid, or paste form and trance of storm water. AWPA Standard M4 contains instruc- are applied into treatment holes that are drilled deeply into tions for the care of pressure-treated wood after treatment. the wood. They are similar (and in some cases identical) to Surface Applications the surface-applied treatments or pastes. Boron is the most The simplest treatment is to apply the preservative to the common active ingredient, but fluoride and copper have also wood with a brush or by spraying. Preservatives that are been used. In timbers, deep holes are drilled perpendicular thoroughly liquid when cold should be selected, unless it is to the upper face on either side of checks. In round piles, possible to heat the preservative. When practical, the preser- steeply sloping holes are drilled across the grain to vative should be flooded over the wood rather than merely maximize the chemical diffusion and minimize the number painted. Every check and depression in the wood should of holes needed. The treatment holes are plugged with tight be thoroughly filled with the preservative, because any un- fitting treated wooden plugs or removable plastic plugs. treated wood left exposed provides ready access for fungi. Plugs with grease fittings are also available so that the paste Rough lumber may require as much as 40 L of preservative can be reapplied without removing the plug. per 100 m2 (10 gallons per 1,000 ft2) of surface, but Solid rod treatments have advantages in environmentally surfaced lumber requires considerably less. The transverse sensitive areas or in applications where the treatment hole penetration obtained will usually be less than 2.5 mm (0.1 can only be drilled at an upward angle. However, the chemi- in.), although in easily penetrated species, end-grain (longi- cal may not diffuse as rapidly or for as great a distance tudinal) penetration is considerably greater. The additional as compared to a liquid form. Solid forms may be less life obtained by such treatments over that of untreated wood mobile because diffusible treatments require moisture to will be affected greatly by the conditions of service. For move through wood. Concentrated liquid borates may also wood in contact with the ground, service life may be from be poured into treatment holes and are sometimes used in 1 to 5 years. conjunction with the rods to provide an initial supply of For brush or spray applications, copper naphthenate in oil is moisture. When the moisture content falls below 20%, little the preservative that is most often used. The solution should chemical movement occurs, but fortunately growth of decay contain 1% to 2% elemental copper. Copper naphthenate is fungi is substantially arrested below 30% moisture. Because available as a concentrate or in a ready-to-use solution in there is some risk that rods installed in a dry section of a gallon and drum containers. Borate solutions can also be timber would not diffuse to an adjacent wet section, some sprayed or brushed into checks or splits. However, because experience in proper placement of the treatment holes is they are not fixed to the wood they can be leached during necessary. The diffusible treatments do not move as far in the wood as do fumigants, and thus the treatment holes must

15–22 Chapter 15 Wood Preservation be spaced more closely. A study of borate diffusion in tim- liquid fumigant that decomposes in the wood to form the bers of several wood species reported that diffusion along active ingredient MITC. Granular dazomet (tetrahydro-3, the grain was generally less than 12 cm (5 in.), and diffusion 5-dimethyl-2-H-1,3,5, thiodazine-6-thione) is applied in a across the grain was typically less than 5 cm (2 in.). solid granular form that decomposes to a MITC content of approximately 45%. Dazomet is easy to handle but slower Internal Fumigant Treatments to decompose and release MITC than the solid-melt MITC As with diffusibles, fumigants are applied in liquid or solid or liquid fumigants. Some suppliers recommend the addition form in predrilled holes. However, they then volatilize into of a catalyst such as copper naphthenate to accelerate the a gas that moves through the wood. To be most effective, breakdown process. a fumigant should be applied at locations where it will not readily volatilize out of the wood to the atmosphere. When Best Management Practices fumigants are applied, the timbers should be inspected thor- The active ingredients of various waterborne wood pre- oughly to determine an optimal drilling pattern that avoids servatives (copper, chromium, arsenic, and zinc) are water metal fasteners, seasoning checks, and severely rotted wood. soluble in the treating solution but resist leaching when In vertical members such as piles, holes to receive liquid fu- placed into the wood. This resistance to leaching is a result migant should be drilled at a steep angle (45° to 60°) down- of chemical stabilization (or fixation) reactions that render ward toward the center of the member, avoiding seasoning the toxic ingredients insoluble in water. The mechanism and checks. The holes should be no more than 1.2 m (4 ft) apart requirements for the stabilization reactions differ, depending and arranged in a spiral pattern. With horizontal timbers, the on the type of wood preservative. holes can be drilled straight down or slanted. As a rule, the holes should be extended to within about 5 cm (2 in.) of the For each type of preservative, some reactions occur very bottom of the timber. If strength is not jeopardized, holes rapidly during pressure treatment, while others may take can be drilled in a cluster or in pairs to accommodate the re- days or even weeks, depending on storage and processing quired amount of preservative. If large seasoning checks are after treatment. If the treated wood is placed in service be- present, the holes should be drilled on each side of the mem- fore these fixation reactions have been completed, the initial ber to provide better distribution. As soon as the fumigant release of preservative into the environment may be much is injected, the hole should be plugged with a tight-fitting greater than if the wood has been conditioned properly. treated wood dowel or removable plastic plug. For liquid With oil-type preservatives, preservative bleeding or ooz- fumigants, sufficient room must remain in the treating hole ing out of the treated wood is a particular concern. This so the plug can be driven without displacing the chemical problem may be apparent immediately after treatment. Such out of the hole. The amount of fumigant needed and the size members should not be used in bridges over water or other and number of treating holes required depends upon the tim- aquatic applications. In other cases, the problem may not ber size. Fumigants will eventually diffuse out of the wood, become obvious until after the product has been exposed to allowing decay fungi to recolonize. Fortunately, additional heating by direct sunlight. This problem can be minimized fumigant can be applied to the same treatment hole. Fumi- by using treatment practices that remove excess preservative gant treatments are generally more toxic and more difficult from the wood. to handle than are diffusible treatments. Some are classified as restricted-use pesticides by the U.S. EPA. Best management practice (BMP) standards have been developed to ensure that treated wood is produced in a way One of the oldest and most effective fumigants is chloropic- that will minimize environmental concerns. The Western rin (trichloronitromethane). Chloropicrin is a liquid and has Wood Preservers Institute (WWPI) has developed guidelines been found to remain in wood for up to 20 years; however, for treated wood used in aquatic environments. Although a 10-year retreatment cycle is recommended, with regular these practices have not yet been adopted by the industry inspection. Chloropicrin is a strong eye irritant and has high in all areas of the United States, purchasers can require that volatility. Due to chloropicrin’s hazardous nature, it should these practices be followed. Commercial wood treatment be used in areas away from buildings permanently inhabited firms are responsible for meeting conditions that ensure by humans or animals. During application, workers must stabilization and minimize bleeding of preservatives, but wear protective gear, including a full face respirator. Me- persons buying treated wood should make sure that the firms thylisothiocyante (MITC) is the active ingredient in several have done so. fumigants, but is also available in a solid-melt form that is 97% actives. The solid-melt MITC is supplied in aluminum Consumers can take steps to ensure that wood will be treat- tubes. After the treatment hole is drilled the cap is removed ed according to the BMPs. Proper stabilization may take from the tube, and the entire tube is placed into the whole. time, and material should be ordered well before it is needed This formulation provides ease of handling and applica- so that the treater can hold the wood while it stabilizes. If tion to upward drilled sloping treatment holes. Metham consumers order wood in advance, they may also be able to sodium (sodium N-methldithiocarbamate) is a widely used store it under cover, allowing further drying and fixation. In general, allowing the material to air dry before it is used is

15–23 General Technical Report FPL–GTR–190 a good practice for ensuring fixation, minimizing leaching, Pentachlorophenol, Creosote, and Copper and reducing risk to construction personnel. With all preser- Naphthenate vatives, the wood should be inspected for surface residue, For creosote, the BMPs stipulate use of an expansion bath and wood with excessive residue should not be placed in and final steaming period at the end of the charge. service. Expansion Bath—Following the pressure period, the creo- CCA sote should be heated to a temperature 6 to 12 °C (10 to The risk of chemical exposure from wood treated with 20 °F) above the press temperatures for at least 1 h. Creo- CCA is minimized after chemical fixation reactions lock sote should be pumped back to storage and a minimum the chemical in the wood. The treating solution contains gauge vacuum of –81 kPa (24 inHg) should be applied for at hexavalent chromium, but the chromium reduces to the least 2 h. less toxic trivalent state within the wood. This process of Steaming—After the pressure period and once the creosote chromium reduction also is critical in fixing the arsenic and has been pumped back to the storage tank, a vacuum of not copper in the wood. Wood treated with CCA should not be less than –74 kPa (22 inHg) is applied for at least 2 h to re- immersed or exposed to prolonged wetting until the fixation cover excess preservative. The vacuum is then released back process is complete or nearly complete. The rate of fixation to atmospheric pressure and the charge is steamed for 2 to depends on temperature, taking only a few hours at 66 °C 3 h. The maximum temperature during this process should (150 °F) but weeks or even months at temperatures below not exceed 116 °C (240 °F). A second vacuum of not less 16 °C (60 °F). Some treatment facilities use kilns, steam, or than –74 kPa (22 inHg) is then applied for a minimum of hot-water baths to accelerate fixation. 4 h. The BMP guideline for CCA stipulates that the wood should The BMPs for copper naphthenate are similar to those for be air seasoned, kiln dried, steamed, or subjected to a hot- creosote and pentachlorophenol. The recommended treat- water bath after treatment. It can be evaluated with the ment practices for treatment in heavy oil include using an AWPA chromotropic acid test to determine whether fixation expansion bath, or final steaming, or both, similar to that is complete. described for creosote. When No. 2 fuel oil is used as the ACZA and ACQ–B solvent, the BMPs recommend using a final vacuum for at The key to achieving stabilization with ACZA and ACQ–B least 1 h. is to allow ammonia to volatilize. This can be accomplished Handling and Seasoning of Timber after Treatment by air or kiln drying. The BMPs require a minimum of Treated timber should be handled with sufficient care to 3 weeks of air drying at temperatures higher than 16 °C avoid breaking through the treated shell. The use of pikes, (60 °F). Drying time can be reduced to 1 week if the ma- cant hooks, picks, tongs, or other pointed tools that dig terial is conditioned in the treatment cylinder. At lower deeply into the wood should be prohibited. Handling heavy temperatures, kiln drying or heat is required to complete loads of lumber or sawn timber in rope or cable slings can fixation. There is no commonly used method to determine crush the corners or edges of the outside pieces. Breakage the degree of stabilization in wood treated with ACZA or or deep abrasions can also result from throwing or dropping ACQ–B, although wood that has been thoroughly dried is the lumber. If damage results, the exposed areas should be acceptable. If the wood has a strong ammonia odor, fixation retreated, if possible. is not complete. Wood treated with preservative oils should generally be ACQ–C, ACQ–D, and Copper Azole installed as soon as practicable after treatment to minimize Proper handling and conditioning of the wood after treat- lateral movement of the preservative, but sometimes cleanli- ment helps minimize leaching and potential environmental ness of the surface can be improved by exposing the treated impacts for these preservatives. Amine (and ammonia in wood to the weather for a limited time before installation. some cases) keeps copper soluble in these treatment solu- Lengthy, unsheltered exterior storage of treated wood before tions. The mechanism of copper’s reaction in the wood is installation should be avoided. Treated wood that must be not completely understood but appears to be strongly influ- stored before use should be covered for protection from the enced by time, temperature, and retention levels. As a gener- sun and weather. al rule, wood that has been thoroughly dried after treatment is properly stabilized. With waterborne preservatives, seasoning after treatment is important for wood that will be used in buildings or other Copper stabilization in the copper azole CA–B formulation places where shrinkage after placement in the structure is extremely rapid (within 24 h) at the UC3B retention of would be undesirable. Injecting waterborne preservatives –3 –3 1.7 kg m (0.10 lb ft ) but slows considerably at higher puts large amounts of water into the wood, and considerable retentions unless the material is heated to accelerate fixation. shrinkage is to be expected as subsequent seasoning takes place. For best results, the wood should be dried to

15–24 Chapter 15 Wood Preservation approximately the moisture content it will ultimately penetrated for waterborne preservatives. The requirements reach in service. During drying, the wood should be care- vary, depending on the species, size, class, and specified fully piled and, whenever possible, restrained by sufficient retention levels. weight on the top of the pile to prevent warping. Preservative retentions are typically expressed on the basis of the mass of preservative per unit volume of wood within Quality Assurance for Treated Wood a prescribed assay zone. The retention calculation is not Treating Conditions and Specifications based on the volume of the entire pole or piece of lumber. Specifications on the treatment of various wood products by For example, the assay zone for Southern Pine poles is be- pressure processes have been developed by AWPA. These tween 13 and 51 mm (0.5 and 2.0 in.) from the surface. To specifications limit pressures, temperatures, and time of con- determine the retention, a boring is removed from the assay ditioning and treatment to avoid conditions that will cause zone and analyzed for preservative concentration. The pre- serious injury to the wood. The specifications also contain servatives and retention levels listed in the AWPA Commod- minimum requirements for preservative penetration and ity Standards and ICC–ES evaluation reports are shown in retention levels and recommendations for handling wood Table 15–1. The current issues of these specifications should after treatment to provide a quality product. Specifications be referenced for up-to-date recommendations and other de- are broad in some respects, allowing the purchaser some tails. In many cases, the retention level is different depend- latitude in specifying the details of individual requirements. ing on species and assay zone. Higher preservative retention However, the purchaser should exercise great care so as not levels are specified for products to be installed under severe to hinder the treating plant operator from doing a good treat- climatic or exposure conditions. Heavy-duty transmis- ing job and not to require treating conditions so severe that sion poles and items with a high replacement cost, such as they will damage the wood. structural timbers and house foundations, are required to be treated to higher retention levels. Correspondingly, deeper Penetration and Retention penetration or heartwood limitations are also necessary for Penetration and retention requirements are equally impor- the same reasons. It may be necessary to increase retention tant in determining the quality of preservative treatment. levels to ensure satisfactory penetration, particularly when Penetration levels vary widely, even in pressure-treated ma- the sapwood is either unusually thick or is somewhat resis- terial. In most species, heartwood is more difficult to pen- tant to treatment. To reduce bleeding of the preservative, etrate than sapwood. In addition, species differ greatly in the however, it may be desirable to use preservative-oil reten- degree to which their heartwood may be penetrated. Incising tion levels less than the stipulated minimum. Older specifi- tends to improve penetration of preservative in many refrac- cations based on treatment to refusal do not ensure adequate tory species, but those highly resistant to penetration will penetration or retention of preservative, should be avoided, not have deep or uniform penetration even when incised. and must not be considered as a substitute for results-type Penetration in unincised heartwood faces of these species specification in treatment. may occasionally be as deep as 6 mm (1/4 in.) but is often not more than 1.6 mm (1/16 in.). Inspection of Treatment Quality AWPA standards specify how charges of treated wood Experience has shown that even slight penetration has some should be inspected to ensure conformance to treatment value, although deeper penetration is highly desirable to standards. Inspections are conducted by the treating com- avoid exposing untreated wood when checks occur, par- pany and also should be routinely conducted by independent ticularly for important members that are costly to replace. third-party inspection agencies. These third-party agencies The heartwood of coastal Douglas-fir, southern pines, and verify for customers that the wood was properly treated in various hardwoods, although resistant, will frequently show accordance with AWPA standards. The U.S. Department of transverse penetrations of 6 to 12 mm (1/4 to 1/2 in.) and Commerce American Lumber Standard Committee (ALSC) sometimes considerably more. accredits third-party inspection agencies for treated-wood Complete penetration of the sapwood should be the goal products. Quality control overview by ALSC-accredited in all pressure treatments. It can often be accomplished in agencies is preferable to simple treating plant certificates or small-size timbers of various commercial woods, and with other claims of conformance made by the producer without skillful treatment, it may often be obtained in piles, ties, and inspection by an independent agency. Updated lists of ac- structural timbers. Practically, however, the operator cannot credited agencies can be obtained from the ALSC website at always ensure complete penetration of sapwood in every www.alsc.org. Each piece of treated wood should be marked piece when treating large pieces of round material with thick with brand, ink stamp, or end-tag that shows the logo of an sapwood (such as poles and piles). Therefore, specifications accredited inspection agency and other information required permit some tolerance. For instance, AWPA Processing and by AWPA standards (Fig. 15–6). Other important informa- Treatment Standard T1 for Southern Pine poles requires tion that should be shown includes the type of preservative, that 89 mm (3.5 in.) or 90% of the sapwood thickness be preservative retention, and the intended use category

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mobility and limiting the range of environmental contami- nation. Levels of these components in the soil immediately adjacent to treated structures can increase gradually over the years, whereas levels in sediments tended to decline over time. Research indicates that environmental releases from treated wood do not cause measurable impacts on the abun- dance or diversity of aquatic invertebrates adjacent to the structures. In most cases, levels of preservative components were below concentrations that might be expected to affect aquatic life. Samples with elevated levels of preservative components tended to be limited to fine sediments beneath stagnant or slow-moving water where the invertebrate com- munity is not particularly intolerant to pollutants. Conditions with a high potential for leaching and a high potential for metals to accumulate are the most likely to af- Figure 15–6. Typical end tag for preservative-treated fect the environment (Fig. 15–7). These conditions are most lumber conforming to the ALSC accreditation likely to be found in boggy or marshy areas with little water program. exchange. Water at these sites has low pH and high organic acid content, increasing the likelihood that preservatives (exposure condition). Purchasers may also elect to have an will be leached from the wood. In addition, the stagnant wa- independent inspector inspect and analyze treated products ter prevents dispersal of any leached components of preser- to ensure compliance with the specifications—recom- vatives, allowing them to accumulate in soil, sediments, and mended for treated-wood products used for critical struc- organisms near the treated wood. Note that all construction tures. Railroad companies, utilities, and other entities that materials, including alternatives to treated wood, have some purchase large quantities of treated timber usually maintain type of environmental impact. In addition to environmental their own inspection services. releases from leaching and maintenance activities, the alternatives may have greater impacts and require greater energy Effects on the Environment consumption during production. Preservatives intended for use outdoors have mechanisms Recycling and Disposal of Treated that are intended to keep the active ingredients in the wood and minimize leaching. Past studies indicate that a small Wood percentage of the active ingredients of all types of wood Treated wood is not listed as a hazardous waste under Fed- preservatives leach out of the wood. The amount of leaching eral law, and it can be disposed of in any waste management depends on factors such as fixation conditions, preserva- facility authorized under State and local law to manage such tive retention in the wood, product size and shape, type of material. State and local jurisdictions may have additional exposure, and years in service. Ingredients in all preserva- regulations that impact the use, reuse, and disposal of treat- tives are potentially toxic to a variety of organisms at high ed wood and treated-wood construction waste, and users concentrations, but laboratory studies indicate that the levels should check with State and local authorities for any special of preservatives leached from treated wood generally are too regulations relating to treated wood. Treated wood must not low to create a biological hazard. be burned in open fires or in stoves, fireplaces, or residential boilers, because the smoke and ashes may contain toxic In recent years, several studies have been conducted on pre- chemicals. servative releases from structures and on the environmental consequences of those releases. These recent studies of the Treated wood from commercial and industrial uses (con- environmental impact of treated wood reveal several key struction sites, for example) may be burned only in commer- points. All types of treated wood evaluated release small cial or industrial incinerators or boilers in accordance with amounts of preservative components into the environment. State and Federal regulations. Spent railroad ties treated These components can sometimes be detected in soil or with creosote and utility poles treated with pentachlorophe- sediment samples. Shortly after construction, elevated levels nol can be burned in properly equipped facilities to generate of preservative components can sometimes be detected in electricity (cogeneration). As fuel costs and energy demands the water column. Detectable increases in soil and sediment increase, disposal of treated wood in this manner becomes concentrations of preservative components generally are more attractive. Cogeneration poses more challenges for limited to areas close to the structure. Leached preservative wood treated with heavy metals, and particularly for wood components either have low water solubility or react treated with arsenic. In addition to concerns with emissions, with components of the soil or sediment, limiting their the concentration of metals in the ash requires further processing.

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Archer, K.; Lebow, S.T. 2006. Wood preservation. Second edition. Primary wood processing, principals and practice, Walker, J.C.F. ed. The Netherlands: Springer. 596 p. Baechler, R.H.; Roth, H.G. 1964. The double-diffusion method of treating wood: a review of studies. Forest Prod- ucts Journal. 14(4): 171–178. Baechler, R.H.; Blew, J.O.; Roth, H.G. 1962. Studies on the assay of pressure-treated lumber. Proceedings of American Wood Preservers’ Association. 58: 21–34. Baechler, R.H.; Gjovik, L.R.; Roth, H.G. 1969. Assay zones for specifying preservative-treated Douglas-fir and Southern Pine timbers. Proceedings of American Wood Preservers’ Figure 15–7. Wood preservative leaching, environmen- Association. 65: 114–123. tal mobility, and effects on aquatic insects were evalu- Baechler, R.H.; Gjovik, L.R.; Roth, H.G. 1970. Marine ated at this wetland boardwalk in western Oregon. tests on combination-treated round and sawed specimens. Proceedings of American Wood Preservers’ Association. As with many materials, reuse of treated wood may be a vi- 66: 249–257. able alternative to disposal. In many situations treated wood Barnes, M.H., ed. 2007. Wood protection 2006. Publication removed from its original application retains sufficient du- No. 7229. Madison, WI: Forest Products Society. 388 p. rability and structural integrity to be reused in a similar application. Generally, regulatory agencies also recognize that Blew, J.O.; Davidson, H.L. 1971. Preservative retentions treated wood can be reused in a manner that is consistent and penetration in the treatment of white fir. Proceedings of with its original intended end use. American Wood Preservers’ Association. 67: 204–221. The potential for recycling preservative-treated wood de- Boone, R.S.; Gjovik, L.R.; Davidson, H.L. 1976. Treatment pends on several factors, including the type of preservative of sawn hardwood stock with double-diffusion and modified treatment and the original use. Researchers have demon- double-diffusion methods. Res. Pap. FPL–RP–265. Madi- strated that wood treated with heavy metals can be chipped son, WI: U.S. Department of Agriculture, Forest Service, or flaked and reused to form durable panel products or Forest Products Laboratory. wood–cement composites. However, this type of reuse has Brooks, K.M. 2000. Assessment of the environmental not yet gained commercial acceptance. Techniques for ex- effects associated with wooden bridges preserved with traction and reuse of the metals from treated wood have also creosote, pentachlorophenol or chromated-copper-arsenate. been proposed. These include acid extraction, fungal degra- Res. Pap. FPL–RP–587. Madison, WI: U.S. Department of dation, bacterial degradation, digestion, steam explosion, or Agriculture, Forest Service, Forest Products Laboratory. some combination of these techniques. All these approaches 100 p. show some potential, but none is currently economical. In most situations landfill disposal remains the least expensive Cassens, D.L.; Johnson, B.R.; Feist, W.C.; De Groot, R.C. option. For treated wood used in residential construction, 1995. Selection and use of preservative-treated wood. one of the greatest obstacles is the lack of an efficient pro- Publication N. 7299. Madison, WI: Forest Products Society. cess for collecting and sorting treated wood. This is less of a Crawford, D.M; Woodward, B.M.; Hatfield, C.A. 2002. problem for products such as railroad ties and utility poles. Comparison of wood preservative in stake tests. 2000 Prog- ress Report. Res. Note FPL–RN–02. Madison, WI: U.S. References Department of Agriculture, Forest Service, Forest Products AWPA. [Current edition]. Annual proceedings. (Reports of Laboratory. preservations and treatment committees containing informa- Eaton, R.A.; Hale, M.D.C. 1993. Wood: decay, pests and tion on new wood preservatives considered in the develop- protection. New York, NY: Chapman & Hall. ment of standards). Birmingham, AL: American Wood Pro- tection Association. Forest Products Laboratory. Environmental impact of preservative treated wood in a wetland boardwalk. Res. Pap. AWPA. 2008. Book of standards. (Includes standards on FPL–RP–582. Madison, WI: U.S. Department of Agricul- preservatives, treatments, methods of analysis, and inspec- ture, Forest Service, Forest Products Laboratory. 126 p. tion.) Birmingham, AL: American Wood Protection Associa- tion.

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Gaby, L.I.; Gjovik, L.R. 1984. Treating and drying com- Richardson, B.A. 1993. Wood preservation. Second edition. posite lumber with waterborne preservatives: Part I. Short London: Chapman and Hall. 226 p. specimen testing. Forest Products Journal. 34(2): 23–26. Schlultz, T.P.; Militz, H.; Freeman, M.H.; Goodell, B.; Nich- Gjovik, L.R.; Baechler, R.H. 1970. Treated wood founda- olas, D.D.; eds. 2008. Development of commercial wood tions for buildings. Forest Products Journal. 20(5): 45–48. preservatives. ACS Symposium Series 982. Washington, DC: American Chemical Society. 655 p. Gjovik, L.R.; Davidson, H.L. 1975. Service records on treated and untreated posts. Res. Note FPL–068. Madison, Western Wood Preservers Institute. 2006. Best management WI: U.S. Department of Agriculture, Forest Service, Forest practices for the use of treated wood in aquatic environ- Products Laboratory. ments. Vancouver, WA: Western Wood Preservers Institute. 34 p. Gjovik, L.R.; Johnson, D.B.; Kozak, V.; [and others]. 1980. Biologic and economic assessment of pentachlorophenol, Western Wood Preservers Institute. 2006. Treated wood in inorganic arsenicals, and creosote. Vol. I: Wood preserva- aquatic environments. Vancouver, WA: Western Wood Pre- tives. Tech. Bull 1658–1. Washington, DC: U.S. Department servers Institute. 32 p. of Agriculture, in cooperation with State Agricultural Exper- imental Stations, Cooperative Extension Service, other state agencies and the Environmental Protection Agency. Groenier, J.S.; Lebow, S. 2006. Preservative-treated wood and alternative products in the Forest Service. Tech. Rep. 0677–2809–MTDC. Missoula, MT: U.S. Department of Agriculture, Forest Service, Missoula Technology and De- velopment Center. 44 p. Hunt, G.M.; Garratt, G.A. 1967. Wood preservation. Third edition. The American Forestry Series. New York, NY: Mc- Graw–Hill. ICC–ES. Evaluation Reports, Section 06070–wood treatment. Whittler, CA: ICC Evaluation Service, Inc. www.icc-es.org. Johnson, B.R.; Gutzmer, D.I. 1990. Comparison of preservative treatments in marine exposure of small wood panels. Res. Note FPL–RN–0258. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. Lebow, S. 1996. Leaching of wood preservative components and their mobility in the environment—summary of perti- nent literature. Gen. Tech. Rep. FPL–GTR–93. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. Lebow, S.T.; Foster, D.O. 2005. Environmental concentrations of copper, chromium and arsenic released from a chromated-copper-arsenate (CCA-C) treated wetland boardwalk. Forest Products Journal. 55(2): 62–70. MacLean, J.D. 1952. Preservation of wood by pressure methods. Agric. Handb. 40. Washington, DC: U.S. Department of Agriculture, Forest Service. NFPA. 1982. The all-weather wood foundation. NFPA Tech. Rep. 7. Washington, DC: National Forest Products Association. NFPA. 1982. All-weather wood foundation system, design fabrication installation manual. NFPA report. Washington DC: National Forest Products Association.

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